scientificamerican--2020-10-22--Can a Moon Base Be Safe for Astronauts?

Can a Moon Base Be Safe for Astronauts?

On August 4 , 1972 , the sun unleashed an incandescent whip of energy from its surface and flung it toward the planets .
It was accompanied by a seething cloud of plasma called a coronal mass ejection , which traversed the nearly 150 million kilometers between sun and Earth in just more than half a day—still the fastest-known arrival time for such outbursts—to briefly bathe our planet in cosmic fire .
Earth ’ s shielding magnetosphere crumpled and shrunk by two thirds , sending powerful geomagnetic currents rippling through the planet .
Dazzling displays of “ northern lights ” @ @ @ @ @ @ @ power lines strained as far south as Texas .
Off the southern coast of Haiphong , North Vietnam , the seas churned as the celestial disturbance prematurely detonated some two dozen U.S. Navy sea mines .
The geomagnetic storm is one of the most violent solar events in recorded history , certainly the most violent of the space age .
The astronauts of Apollo 16 had been home about three months from their lunar foray , and those of Apollo 17 were still preparing for their December launch .
The fact that the @ @ @ @ @ @ @ final crewed moon missions was simply a matter of chance .
If the members of either crew had been in space during the solar storm , especially if they had been traversing the portion of the “ cislunar ” region between Earth and the moon that lies outside the magnetosphere , they would have been exposed to a potentially deadly dose of radiation .
We got lucky in 1972 .
And in terms of space-based hazards , that luck has largely held throughout humanity ’ s off-world excursions .
To date , the @ @ @ @ @ @ @ were the three cosmonauts of Soyuz 11 , who asphyxiated because of faulty hardware as their spacecraft began its descent to Earth .
Yet despite what most estimates would seem to consider a near-sterling safety record , today the prospect of venturing back beyond low-Earth orbit somehow seems more daunting—more dangerous—than it did when the Apollo program ended .
Equipped with more knowledge than ever about the environs beyond our home , we now seem more reluctant to leave it .
Maybe we know too much .
Politics , money and uneven federal @ @ @ @ @ @ @ since Richard Nixon has sent humans back to the moon .
Some lunar exploration advocates also sense more philosophical reasons , however .
We understand , better than at any point in the space age , what can happen to us out there .
Is making the journey worth it ?
We watch our own planet burn , and we witness almost unimaginable beauty recorded by the sensors of our solar-system-touring robots , and we wonder whether human lives should be on the line in the name of exploring beyond Earth .
Space @ @ @ @ @ @ @ to venture past our world ’ s upper atmosphere will die painfully without a life-support system .
Even with adequate life support , the sun could still kill spacefarers if it lets loose at just the wrong instant while they are beyond the magnetosphere ’ s protective bubble .
Deep space could kill us , too— even from afar : particles and radiation emanating from exploding stars and active galaxies become , when they arrive in our vicinity , harmful cosmic rays that can rend DNA at the seams to spark cancer and @ @ @ @ @ @ @ latter threat is only now becoming clear .
On September 25 an international team of scientists working with China ’ s Chang ’ e 4 lander and Yutu 2 rover announced the moon is constantly bombarded by showers of dangerous cosmic rays .
“ A New Problem for Astronauts , ” read part of a headline at the Web site ExtremeTech .
“ Radiation Levels on the Moon Are Alarmingly High , ” said a site called Interesting Engineering .
“ New Measurements Show Moon Has Hazardous Radiation Levels , ” the Associated @ @ @ @ @ @ @ lunar scientist and space-exploration advocate at the University of Notre Dame , has hoped to see more people on the moon since the Apollo 17 astronauts departed 48 years ago .
Making that happen , he suspects , might require acknowledging that failure is not only an option—it is inevitable .
“ As we ’ ve seen in testing rockets , failure is where you learn a lot , ” he says .
“ Despite everything you do , you ’ re not going to get rid of all the risks .
That @ @ @ @ @ @ @ , Americans strapped to an American rocket launched from American soil for the first time in nearly a decade .
Could a return to the moon be far off ?
Under the Trump administration ’ s Artemis plan , NASA is angling to send the first woman and the next man to the moon ’ s resource-rich south pole by 2024 .
It is a long shot : The space agency and the contractors it relies on for much of its flight hardware must hasten to finish the arduous task of building massive @ @ @ @ @ @ @ believe Congress has to dramatically increase funding for this to be possible , to say nothing of the uncertainty that would stem from a November 3 victory by Democrats Joe Biden and Kamala Harris in the U.S. presidential election .
NASA administrator Jim Bridenstine says he is optimistic , however .
And a growing community of lunar scientists and private companies are operating as though Artemis will happen , even as the true scopes of the myriad challenges the project faces becomes clear .
“ Everyone has wanted to make progress in their @ @ @ @ @ @ @ Now that there seems to be a real solid direction and a goal , everybody is motivated and working together , ” says Dana Hurley , a space physicist at the Johns Hopkins University Applied Physics Laboratory ( APL ) .
People are working together to allow humans to live and work “ off-planet , ” as Neal likes to put it .
Protecting them from radiation has to be a primary goal .
But just how that would work , and what level of protection is actually necessary , will be a @ @ @ @ @ @ @ .
“ Anybody who is on the NASA side of the aisle is going to say , ‘ First and foremost , we have to preserve the safety of the people engaged , the astronauts , and everything else is secondary.
’ And it should be , ” says Roger Launius , a longtime NASA historian .
“ Nobody disagrees with that .
The question is ‘ What is necessary to ensure that safety ?
’ That ’ s always a hard thing.
” Astronauts on the surface of the moon would face @ @ @ @ @ @ @ than we experience on Earth , says Robert F. Wimmer-Schweingruber of Kiel University in Germany , who co-led the new Chang ’ e 4 study .
That is about two and a half times the radiation level on the International Space Station ( ISS ) .
Earth ’ s thick atmosphere and powerful magnetic field protect us .
The moon is airless , however , and its magnetic field is extremely weak , so it has no shielding .
The cosmic rays are mostly in the form of neutrons , which are large @ @ @ @ @ @ @ particles go ) .
And they can produce secondary particles that do their own damage , much like a cue ball scattering racked billiard balls .
Ironically , the sun protects from this a bit , says George Ho , a heliophysicist at APL .
When our star is undergoing the active phase of its 11-year cycle , it unleashes more radiation , like it did in that nasty 1972 storm .
These harmful emanations can , to some degree , safeguard Earth and the other planets by deflecting a portion of the @ @ @ @ @ @ @ performed by the Chang ’ e 4 mission occurred during an extraordinarily quiescent solar phase , Ho adds .
“ We ’ ve done so much better since the Apollo days .
We look at the sun continuously now , ” Ho says .
“ We can forecast and say , ‘ Hey , the next seven days will be bad for people doing EVAs [ extravehicular activities ] .
’ And for solar particle events , a few millimeters of aluminum can shield from those.
” Because they can penetrate such thin @ @ @ @ @ @ @ dangerous than run-of-the-mill solar particles .
Radiation-blocking material such as lead offers little help because it still produces secondary particles that are also dangerous .
Many scientists expect that visitors to the moon , especially the first few crews , will stay for only a few days or , at most , a couple of weeks .
The cumulative radiation dose for such short stays would be manageable .
Longer-term outposts , such as moon bases and lunar-orbiting space stations envisaged by multiple space programs , will need a plan , however .
@ @ @ @ @ @ @ yet advocates such as Neal say they will only come to fruition if countries work together , not in competition .
The most obvious solution to high levels of radiation at the lunar surface is to avoid dwelling there .
Wimmer-Schweingruber says underground habitats could protect moon dwellers from many harmful particles .
Lunar visitors should plan to build habitats at least 80 centimeters ( about two and a half feet ) beneath the surface , he says .
To do so , they will want to bring bulldozers—or at least beefy rovers @ @ @ @ @ @ @ , a physicist at the Planetary Science Institute , imagines people living inside lava tubes , which are hollow deposits left behind by ancient magma flows .
“ It ’ s kind of a double whammy , because it ’ s not only going to protect you from radiation but also protect you from micrometeoroid impacts , ” she says .
Sungwoo Lim , a physicist at the Open University , based in England , has published research describing how to use microwaves to sinter lunar regolith .
This work raises the distinct @ @ @ @ @ @ @ building material the ancient Sumerian way : by baking dirt into bricks .
At the Massachusetts Institute of Technology , aeronautics researcher Dava Newman and her graduate student Cody Paige are working on future space suits built from new advanced materials .
Polyethylene—basic plastic—turns out to be a great radiation shield because it is so full of hydrogen , which absorbs the heavy neutrons in cosmic rays , Paige says .
Future space suits could further boost their protective capacity by also incorporating aerogels , carbon nanotubes , boron nanotubes and boron shielding @ @ @ @ @ @ @ helpful : because of how neutrons are arrayed inside its atomic nuclei , the substance ’ s cosmic-ray-stopping power is some four orders of magnitude greater than that of hydrogen .
Future space suits have to be lightweight , easy to move in , and better at protecting astronauts from hazards such as micrometeorites and radiation , Newman says .
The current basic space suit weighs about 300 pounds ( 136 kilograms ) , and she wants to bring that down to 90 pounds ( 41 kilograms ) .
“ You ’ re @ @ @ @ @ @ @ you ’ re in a gas-pressurized , bulky shell , ” Newman says .
The next space suit might look and fit more like a wet suit .
Astronauts could don multiple layers like a spring skier and don a radiation-shielding overcoat when the conditions call for it .
Space suits could also add shielding where it is most necessary , covering essential organs but leaving the extremities more exposed .
Astronauts will face three main sources of danger on the moon : radiation , reduced gravity and regolith .
Radiation is the @ @ @ @ @ @ @ is a well-known health hazard , too .
Even when offset by rigorous exercise , astronauts still lose muscle mass and bone density during extended stays in the microgravity environs of the ISS .
The moon ’ s gravity is heftier—about one sixth of Earth ’ s—but long-duration visitors will still experience some of low gravity ’ s deleterious effects .
Se-Jin Lee , a geneticist at the University of Connecticut , is trying to address some of those problems .
After more than 10 years of efforts , he was able to @ @ @ @ @ @ @ ISS last December .
Some of the animals were modified to lack a gene that suppresses muscle growth , some were treated with an experimental drug that works in a similar fashion , and others served as unmodified controls .
The modified and treated mice not only maintained their muscle mass in space but even bulked up and had better bone density , compared with the untreated ones , Lee found .
Although a drug based on this research remains far off for humans , the work suggests that astronauts might someday be @ @ @ @ @ @ @ the worst health effects of reduced gravity .
The gene that suppresses muscle growth produces a protein called myostatin , which usually works to balance muscle mass with fat .
A molecule that keeps the two in equilibrium would benefit animals trying to maintain enough muscle to hunt or run away while also preventing them from accumulating it in excess , which is more costly to maintain .
“ For humans , I think this is an evolutionary vestige , ” Lee says of the molecule .
“ We don ’ t really @ @ @ @ @ @ @ We all have refrigerators ; we live in homes with electricity ; we don ’ t have to escape from predators .
That ’ s why I argue that this particular system is so attractive for drugs.
” Even if astronauts can avoid radiation exposure and muscle degeneration , the moon ’ s surficial soil—called regolith—itself poses another tricky problem .
Composed of jagged , microscopic shards of rock , moon dust is like a more abrasive and irritating talcum powder : it gets into everything , from astronaut lungs to tiny machine @ @ @ @ @ @ @ flies around when a spacecraft lands or launches , turning landing zones into a buckshot-blasted scouring pad , Watkins notes .
“ The bigger concern becomes when you start to land multiple spacecraft in the same area .
You really have to worry about how far away you land because of that dust , ” she says .
“ Imagine it flying at one kilometer per second .
It ’ s going to do some damage , so figuring out ways to mitigate that is a big area of concern right now.
” @ @ @ @ @ @ @ Stronger Like many enthusiastic lunar scientists , M.I.T.
’ s Newman notes that the next wave of space exploration is a form of soft diplomacy .
“ This is about the potential of the world working together , ” she says .
Launius , like many others , views the moon as akin to Antarctica , which contains multiple international scientific stations .
It is difficult and dangerous to access , but people do it all the time , cycling in and out in small crews .
“ We can do camping trips @ @ @ @ @ @ @ .
“ We can go up and spend a few days ; take everything you need with you .
There ’ s not any reason to think we don ’ t have the capability to put a lunar base up and stay there for some period of time .
But here ’ s the problem : Fundamentally , going into space with humans is about becoming a multiplanetary species .
If that ’ s not the reason , then why are we doing it ?
Once you do that , we ’ re @ @ @ @ @ @ @ station.
” It is hard to talk in practical terms about such grand ideas , Launius says .
And right now , when multiple countries are planning moon bases and space stations , practicality is rearing its head .
Space travel is more possible than ever , and we know more about it than ever , so the danger is more clear and present than it was in the past .
What is more , Launius believes the U.S. is more averse to risk now than it was during the Apollo age .
@ @ @ @ @ @ @ , ” he says .
“ If I ’ m standing on the corner waiting to cross , and I see a car 100 yards [ 91 meters ] away , I may decide I can make that .
But the person next to me may not .
That ’ s an understandable problem , and it ’ s different from person to person .
NASA is cautious because they ’ ve had some really close calls , and they ’ ve had some accidents in which they ’ ve lost astronauts .
@ @ @ @ @ @ @ little more risk-averse now , as a society.
” The space agency is also a huge ship , powered by taxpayers and steered by politics .
Exploration advocates have seen moon-return programs announced , hyped , planned and then canceled several times since the 1970s .
Decades of uncertainty are one reason some scientists are so eager to work with the private sector—and vice versa .
Watkins serves on a science advisory panel for Amazon founder Jeff Bezos ’ s space exploration company Blue Origin , and she says the company is keen @ @ @ @ @ @ @ to land and which kinds of experimental equipment to bring .
Private corporations , beholden to stockholders or a few owners , might have a different tolerance for risk than a government agency that answers to the many .
While some exploration advocates argue that NASA needs to dream bigger or cut red tape out of the way , many scientists say simply realizing that space can kill us is not the problem .
What does not kill us could make us stronger .
“ It ’ s not that people aren ’ @ @ @ @ @ @ @ to the lunar south pole is big , ” Watkins says of NASA ’ s planned Artemis mission to land humans on the moon .
“ We just have more knowledge , which isn ’ t a bad thing at all .
We know more , and that means we can also prepare better .
”

On August 4, 1972, the sun unleashed an incandescent whip of energy from its surface and flung it toward the planets. It was accompanied by a seething cloud of plasma called a coronal mass ejection, which traversed the nearly 150 million kilometers between sun and Earth in just more than half a day—still the fastest-known arrival time for such outbursts—to briefly bathe our planet in cosmic fire.
Earth’s shielding magnetosphere crumpled and shrunk by two thirds, sending powerful geomagnetic currents rippling through the planet. Dazzling displays of “northern lights” stretched down to Spain, and overloaded power lines strained as far south as Texas. Off the southern coast of Haiphong, North Vietnam, the seas churned as the celestial disturbance prematurely detonated some two dozen U.S. Navy sea mines. The geomagnetic storm is one of the most violent solar events in recorded history, certainly the most violent of the space age.
The astronauts of Apollo 16 had been home about three months from their lunar foray, and those of Apollo 17 were still preparing for their December launch. The fact that the solar outburst happened between the penultimate and final crewed moon missions was simply a matter of chance. If the members of either crew had been in space during the solar storm, especially if they had been traversing the portion of the “cislunar” region between Earth and the moon that lies outside the magnetosphere, they would have been exposed to a potentially deadly dose of radiation.
We got lucky in 1972. And in terms of space-based hazards, that luck has largely held throughout humanity’s off-world excursions. To date, the only humans to actually die in space were the three cosmonauts of Soyuz 11, who asphyxiated because of faulty hardware as their spacecraft began its descent to Earth. Yet despite what most estimates would seem to consider a near-sterling safety record, today the prospect of venturing back beyond low-Earth orbit somehow seems more daunting—more dangerous—than it did when the Apollo program ended. Equipped with more knowledge than ever about the environs beyond our home, we now seem more reluctant to leave it. Maybe we know too much.
Failure Is an Option
Politics, money and uneven federal directives can all explain why no president since Richard Nixon has sent humans back to the moon. Some lunar exploration advocates also sense more philosophical reasons, however. We understand, better than at any point in the space age, what can happen to us out there. Is making the journey worth it? We watch our own planet burn, and we witness almost unimaginable beauty recorded by the sensors of our solar-system-touring robots, and we wonder whether human lives should be on the line in the name of exploring beyond Earth. Space can kill us. Anyone who dares to venture past our world’s upper atmosphere will die painfully without a life-support system. Even with adequate life support, the sun could still kill spacefarers if it lets loose at just the wrong instant while they are beyond the magnetosphere’s protective bubble. Deep space could kill us, too— even from afar: particles and radiation emanating from exploding stars and active galaxies become, when they arrive in our vicinity, harmful cosmic rays that can rend DNA at the seams to spark cancer and other maladies.
The severity of this latter threat is only now becoming clear. On September 25 an international team of scientists working with China’s Chang’e 4 lander and Yutu 2 rover announced the moon is constantly bombarded by showers of dangerous cosmic rays. “A New Problem for Astronauts,” read part of a headline at the Web site ExtremeTech. “Radiation Levels on the Moon Are Alarmingly High,”said a site called Interesting Engineering. “New Measurements Show Moon Has Hazardous Radiation Levels,” the Associated Press wrote.
Clive Neal, a lunar scientist and space-exploration advocate at the University of Notre Dame, has hoped to see more people on the moon since the Apollo 17 astronauts departed 48 years ago. Making that happen, he suspects, might require acknowledging that failure is not only an option—it is inevitable. “As we’ve seen in testing rockets, failure is where you learn a lot,” he says. “Despite everything you do, you’re not going to get rid of all the risks. That is a fact.”
Earlier this year, Americans strapped to an American rocket launched from American soil for the first time in nearly a decade. Could a return to the moon be far off? Under the Trump administration’s Artemis plan, NASA is angling to send the first woman and the next man to the moon’s resource-rich south pole by 2024. It is a long shot: The space agency and the contractors it relies on for much of its flight hardware must hasten to finish the arduous task of building massive new rockets and landers. Most experts believe Congress has to dramatically increase funding for this to be possible, to say nothing of the uncertainty that would stem from a November 3 victory by Democrats Joe Biden and Kamala Harris in the U.S. presidential election. NASA administrator Jim Bridenstine says he is optimistic, however. And a growing community of lunar scientists and private companies are operating as though Artemis will happen, even as the true scopes of the myriad challenges the project faces becomes clear.
“Everyone has wanted to make progress in their individual area for a long time. Now that there seems to be a real solid direction and a goal, everybody is motivated and working together,” says Dana Hurley, a space physicist at the Johns Hopkins University Applied Physics Laboratory (APL).
People are working together to allow humans to live and work “off-planet,” as Neal likes to put it. Protecting them from radiation has to be a primary goal. But just how that would work, and what level of protection is actually necessary, will be a question for space agencies—and the astronauts themselves.
“Anybody who is on the NASA side of the aisle is going to say, ‘First and foremost, we have to preserve the safety of the people engaged, the astronauts, and everything else is secondary.’ And it should be,” says Roger Launius, a longtime NASA historian. “Nobody disagrees with that. The question is ‘What is necessary to ensure that safety?’ That’s always a hard thing.”
The Radioactive Moon
Astronauts on the surface of the moon would face between 200 and 1,000 times more radiation than we experience on Earth, says Robert F. Wimmer-Schweingruber of Kiel University in Germany, who co-led the new Chang’e 4 study. That is about two and a half times the radiation level on the International Space Station (ISS). Earth’s thick atmosphere and powerful magnetic field protect us. The moon is airless, however, and its magnetic field is extremely weak, so it has no shielding. The cosmic rays are mostly in the form of neutrons, which are large and heavy (as far as subatomic particles go). And they can produce secondary particles that do their own damage, much like a cue ball scattering racked billiard balls.
Ironically, the sun protects from this a bit, says George Ho, a heliophysicist at APL. When our star is undergoing the active phase of its 11-year cycle, it unleashes more radiation, like it did in that nasty 1972 storm. These harmful emanations can, to some degree, safeguard Earth and the other planets by deflecting a portion of the incoming cosmic rays. The recent measurements performed by the Chang’e 4 mission occurred during an extraordinarily quiescent solar phase, Ho adds.
“We’ve done so much better since the Apollo days. We look at the sun continuously now,” Ho says. “We can forecast and say, ‘Hey, the next seven days will be bad for people doing EVAs [extravehicular activities].’ And for solar particle events, a few millimeters of aluminum can shield from those.”
Because they can penetrate such thin shielding, galactic cosmic rays are more dangerous than run-of-the-mill solar particles. Radiation-blocking material such as lead offers little help because it still produces secondary particles that are also dangerous.
Many scientists expect that visitors to the moon, especially the first few crews, will stay for only a few days or, at most, a couple of weeks. The cumulative radiation dose for such short stays would be manageable. Longer-term outposts, such as moon bases and lunar-orbiting space stations envisaged by multiple space programs, will need a plan, however. Lunar scientists have plenty of ideas, yet advocates such as Neal say they will only come to fruition if countries work together, not in competition.
Subsurface Shelters and ‘Spring Skier’ Space Suits
The most obvious solution to high levels of radiation at the lunar surface is to avoid dwelling there. Wimmer-Schweingruber says underground habitats could protect moon dwellers from many harmful particles. Lunar visitors should plan to build habitats at least 80 centimeters (about two and a half feet) beneath the surface, he says. To do so, they will want to bring bulldozers—or at least beefy rovers with front-end loading attachments.
Ryan Watkins, a physicist at the Planetary Science Institute, imagines people living inside lava tubes, which are hollow deposits left behind by ancient magma flows. “It’s kind of a double whammy, because it’s not only going to protect you from radiation but also protect you from micrometeoroid impacts,” she says.
Sungwoo Lim, a physicist at the Open University, based in England, has published research describing how to use microwaves to sinter lunar regolith. This work raises the distinct possibility that future moon residents could produce building material the ancient Sumerian way: by baking dirt into bricks.
At the Massachusetts Institute of Technology, aeronautics researcher Dava Newman and her graduate student Cody Paige are working on future space suits built from new advanced materials. Polyethylene—basic plastic—turns out to be a great radiation shield because it is so full of hydrogen, which absorbs the heavy neutrons in cosmic rays, Paige says. Future space suits could further boost their protective capacity by also incorporating aerogels, carbon nanotubes, boron nanotubes and boron shielding, she adds. Boron-10 is especially helpful: because of how neutrons are arrayed inside its atomic nuclei, the substance’s cosmic-ray-stopping power is some four orders of magnitude greater than that of hydrogen.
Future space suits have to be lightweight, easy to move in, and better at protecting astronauts from hazards such as micrometeorites and radiation, Newman says. The current basic space suit weighs about 300 pounds (136 kilograms), and she wants to bring that down to 90 pounds (41 kilograms).
“You’re wasting the majority of your energy if you’re in a gas-pressurized, bulky shell,” Newman says. The next space suit might look and fit more like a wet suit. Astronauts could don multiple layers like a spring skier and don a radiation-shielding overcoat when the conditions call for it. Space suits could also add shielding where it is most necessary, covering essential organs but leaving the extremities more exposed.
Bulked-Up Mice and Buckshot Regolith
Astronauts will face three main sources of danger on the moon: radiation, reduced gravity and regolith. Radiation is the most recent concern, yet reduced gravity is a well-known health hazard, too. Even when offset by rigorous exercise, astronauts still lose muscle mass and bone density during extended stays in the microgravity environs of the ISS. The moon’s gravity is heftier—about one sixth of Earth’s—but long-duration visitors will still experience some of low gravity’s deleterious effects.
Se-Jin Lee, a geneticist at the University of Connecticut, is trying to address some of those problems. After more than 10 years of efforts, he was able to send a team of mice to the ISS last December. Some of the animals were modified to lack a gene that suppresses muscle growth, some were treated with an experimental drug that works in a similar fashion, and others served as unmodified controls. The modified and treated mice not only maintained their muscle mass in space but even bulked up and had better bone density, compared with the untreated ones, Lee found.
Although a drug based on this research remains far off for humans, the work suggests that astronauts might someday be able to take a pill to prevent the worst health effects of reduced gravity.
The gene that suppresses muscle growth produces a protein called myostatin, which usually works to balance muscle mass with fat. A molecule that keeps the two in equilibrium would benefit animals trying to maintain enough muscle to hunt or run away while also preventing them from accumulating it in excess, which is more costly to maintain.
“For humans, I think this is an evolutionary vestige,” Lee says of the molecule. “We don’t really need to deal with this anymore. We all have refrigerators; we live in homes with electricity; we don’t have to escape from predators. That’s why I argue that this particular system is so attractive for drugs.”
Even if astronauts can avoid radiation exposure and muscle degeneration, the moon’s surficial soil—called regolith—itself poses another tricky problem. Composed of jagged, microscopic shards of rock, moon dust is like a more abrasive and irritating talcum powder: it gets into everything, from astronaut lungs to tiny machine parts and structural crevices. It also flies around when a spacecraft lands or launches, turning landing zones into a buckshot-blasted scouring pad, Watkins notes.
“The bigger concern becomes when you start to land multiple spacecraft in the same area. You really have to worry about how far away you land because of that dust,” she says. “Imagine it flying at one kilometer per second. It’s going to do some damage, so figuring out ways to mitigate that is a big area of concern right now.”
What Does Not Kill You Makes You Stronger
Like many enthusiastic lunar scientists, M.I.T.’s Newman notes that the next wave of space exploration is a form of soft diplomacy. “This is about the potential of the world working together,” she says.
Launius, like many others, views the moon as akin to Antarctica, which contains multiple international scientific stations. It is difficult and dangerous to access, but people do it all the time, cycling in and out in small crews. “We can do camping trips to the moon,” he says. “We can go up and spend a few days; take everything you need with you. There’s not any reason to think we don’t have the capability to put a lunar base up and stay there for some period of time. But here’s the problem: Fundamentally, going into space with humans is about becoming a multiplanetary species. If that’s not the reason, then why are we doing it? Once you do that, we’re talking not just about a lunar research station.”
It is hard to talk in practical terms about such grand ideas, Launius says. And right now, when multiple countries are planning moon bases and space stations, practicality is rearing its head. Space travel is more possible than ever, and we know more about it than ever, so the danger is more clear and present than it was in the past. What is more, Launius believes the U.S. is more averse to risk now than it was during the Apollo age.
“We all do this risk calculation,” he says. “If I’m standing on the corner waiting to cross, and I see a car 100 yards [91 meters] away, I may decide I can make that. But the person next to me may not. That’s an understandable problem, and it’s different from person to person. NASA is cautious because they’ve had some really close calls, and they’ve had some accidents in which they’ve lost astronauts. But I think we may be a little more risk-averse now, as a society.”
The space agency is also a huge ship, powered by taxpayers and steered by politics. Exploration advocates have seen moon-return programs announced, hyped, planned and then canceled several times since the 1970s. Decades of uncertainty are one reason some scientists are so eager to work with the private sector—and vice versa. Watkins serves on a science advisory panel for Amazon founder Jeff Bezos’s space exploration company Blue Origin, and she says the company is keen to work with scientists to decide where to land and which kinds of experimental equipment to bring. Private corporations, beholden to stockholders or a few owners, might have a different tolerance for risk than a government agency that answers to the many.
While some exploration advocates argue that NASA needs to dream bigger or cut red tape out of the way, many scientists say simply realizing that space can kill us is not the problem. What does not kill us could make us stronger.
“It’s not that people aren’t dreaming big. Sending a crew to the lunar south pole is big,” Watkins says of NASA’s planned Artemis mission to land humans on the moon. “We just have more knowledge, which isn’t a bad thing at all. We know more, and that means we can also prepare better.”


scientificamerican--2020-10-24--COVID-19 Herd Immunity Strategies Could Bring 'Untold Death and Suffering'

In May , the Brazilian city of Manaus was devastated by a large outbreak of COVID-19 .
Hospitals were overwhelmed and the city was digging new grave sites in the surrounding forest .
But by August , something had shifted .
Despite relaxing social-distancing requirements in early June , the city of 2 million people had reduced its number of excess deaths from around 120 per day to nearly zero .
In September , two groups of researchers posted preprints suggesting that Manaus ’ s late-summer slowdown in COVID-19 cases had happened , at least in part , because a @ @ @ @ @ @ @ population had already been exposed to the virus and was now immune .
Immunologist Ester Sabino at the University of São Paulo , Brazil , and her colleagues tested more than 6,000 samples from blood banks in Manaus for antibodies to SARS-CoV-2 .
“ We show that the number of people who got infected was really high—reaching 66 % by the end of the first wave , ” Sabino says .
Her group concluded that this large infection rate meant that the number of people who were still vulnerable to the virus was @ @ @ @ @ @ @ called herd immunity .
Another group in Brazil reached similar conclusions .
Such reports from Manaus , together with comparable arguments about parts of Italy that were hit hard early in the pandemic , helped to embolden proposals to chase herd immunity .
The plans suggested letting most of society return to normal , while taking some steps to protect those who are most at risk of severe disease .
That would essentially allow the coronavirus to run its course , proponents said .
But epidemiologists have repeatedly smacked down such ideas .
@ @ @ @ @ @ @ not a defensible plan , says Kristian Andersen , an immunologist at the Scripps Research Institute in La Jolla , California .
Such an approach would lead to a catastrophic loss of human lives without necessarily speeding up society ’ s return to normal , he says .
“ We have never successfully been able to do it before , and it will lead to unacceptable and unnecessary untold human death and suffering.
” Despite widespread critique , the idea keeps popping up among politicians and policymakers in numerous countries , including Sweden @ @ @ @ @ @ @ States .
US President Donald Trump spoke positively about it in September , using the malapropism “ herd mentality ” .
And even a few scientists have pushed the agenda .
In early October , a libertarian think tank and a small group of scientists released a document called the Great Barrington Declaration .
In it , they call for a return to normal life for people at lower risk of severe COVID-19 , to allow SARS-CoV-2 to spread to a sufficient level to give herd immunity .
People at high risk , @ @ @ @ @ @ @ , could be protected through measures that are largely unspecified .
The writers of the declaration received an audience in the White House , and sparked a counter memorandum from another group of scientists in The Lancet , which called the herd-immunity approach a “ dangerous fallacy unsupported by scientific evidence ” .
Arguments in favour of allowing the virus to run its course largely unchecked share a misunderstanding about what herd immunity is , and how best to achieve it .
Here , Nature answers five questions about the controversial idea .
@ @ @ @ @ @ @ ’ t spread because it keeps encountering people who are protected against infection .
Once a sufficient proportion of the population is no longer susceptible , any new outbreak peters out .
“ You don ’ t need everyone in the population to be immune—you just need enough people to be immune , ” says Caroline Buckee , an epidemiologist at Harvard T.H .
Chan School of Public Health in Boston , Massachusetts .
Typically , herd immunity is discussed as a desirable result of wide-scale vaccination programmes .
High levels of vaccination-induced @ @ @ @ @ @ @ can ’ t receive or sufficiently respond to a vaccine , such as people with compromised immune systems .
Many medical professionals hate the term herd immunity , and prefer to call it “ herd protection ” , Buckee says .
That ’ s because the phenomenon doesn ’ t actually confer immunity to the virus itself—it only reduces the risk that vulnerable people will come into contact with the pathogen .
But public-health experts don ’ t usually talk about herd immunity as a tool in the absence of vaccines .
“ @ @ @ @ @ @ @ it ’ s now used to mean how many people need to get infected before this thing stops , ” says Marcel Salathé , an epidemiologist at the Swiss Federal Institute of Technology in Lausanne .
How do you achieve it ?
Epidemiologists can estimate the proportion of a population that needs to be immune before herd immunity kicks in .
This threshold depends on the basic reproduction number , R0—the number of cases , on average , spawned by one infected individual in an otherwise fully susceptible , well-mixed population , says @ @ @ @ @ @ @ and mathematical modeller at the Chinese University of Hong Kong .
The formula for calculating the herd-immunity threshold is 1–1/R0—meaning that the more people who become infected by each individual who has the virus , the higher the proportion of the population that needs to be immune to reach herd immunity .
For instance , measles is extremely infectious , with an R0 typically between 12 and 18 , which works out to a herd-immunity threshold of 92–94 % of the population .
For a virus that is less infectious ( with a @ @ @ @ @ @ @ would be lower .
The R0 assumes that everyone is susceptible to the virus , but that changes as the epidemic proceeds , because some people become infected and gain immunity .
For that reason , a variation of R0 called the R effective ( abbreviated Rt or Re ) is sometimes used in these calculations , because it takes into consideration changes in susceptibility in the population .
Although plugging numbers into the formula spits out a theoretical number for herd immunity , in reality , it isn ’ t achieved at @ @ @ @ @ @ @ ’ s better to think of it as a gradient , says Gypsyamber D ’ Souza , an epidemiologist at Johns Hopkins University in Baltimore , Maryland .
And because variables can change , including R0 and the number of people susceptible to a virus , herd immunity is not a steady state .
Even once herd immunity is attained across a population , it ’ s still possible to have large outbreaks , such as in areas where vaccination rates are low .
“ We ’ ve seen that play out in @ @ @ @ @ @ @ has spread , ” Salathé says .
“ In local pockets , you start to see a drop in vaccinations , and then you can have local outbreaks which can be very large , even though you ’ ve technically reached herd immunity as per the math.
” The ultimate goal is to prevent people from becoming unwell , rather than to attain a number in a model .
How high is the threshold for SARS-CoV-2 ?
Reaching herd immunity depends in part on what ’ s happening in the population .
Calculations @ @ @ @ @ @ @ the values of R , Kwok says .
In June , he and his colleagues published a letter to the editor in the Journal of Infection that demonstrates this .
Kwok and his team estimated the Rt in more than 30 countries , using data on the daily number of new COVID-19 cases from March .
They then used these values to calculate a threshold for herd immunity in each country ’ s population .
The numbers ranged from as high as 85 % in Bahrain , with its then-Rt of 6.64 , @ @ @ @ @ @ @ Kuwait , where the Rt was 1.06 .
Kuwait ’ s low numbers reflected the fact that it was putting in place lots of measures to control the virus , such as establishing local curfews and banning commercial flights from many countries .
If the country stopped those measures , Kwok says , the herd-immunity threshold would go up .
Herd-immunity calculations such as the ones in Kwok ’ s example are built on assumptions that might not reflect real life , says Samuel Scarpino , a network scientist who studies infectious disease @ @ @ @ @ @ @ .
“ Most of the herd-immunity calculations don ’ t have anything to say about behaviour at all .
They assume there ’ s no interventions , no behavioural changes or anything like that , ” he says .
This means that if a transient change in people ’ s behaviour ( such as physical distancing ) drives the Rt down , then “ as soon as that behaviour goes back to normal , the herd-immunity threshold will change.
” Estimates of the threshold for SARS-CoV-2 range from 10 % to 70 % @ @ @ @ @ @ @ calculate numbers at the lower end of that range rely on assumptions about how people interact in social networks that might not hold true , Scarpino says .
Low-end estimates imagine that people with many contacts will get infected first , and that because they have a large number of contacts , they will spread the virus to more people .
As these ‘ superspreaders ’ gain immunity to the virus , the transmission chains among those who are still susceptible are greatly reduced .
And “ as a result of that , @ @ @ @ @ @ @ threshold ” , Scarpino says .
But if it turns out that anybody could become a superspreader , then “ those assumptions that people are relying on to get the estimates down to around 20 % or 30 % are just not accurate ” , Scarpino explains .
The result is that the herd-immunity threshold will be closer to 60–70 % , which is what most models show ( see , for example , ref .
6 ) .
Looking at known superspreader events in prisons and on cruise ships , it seems @ @ @ @ @ @ @ before slowing down in a captive , unvaccinated population , Andersen says .
At San Quentin State Prison in California , more than 60 % of the population was ultimately infected before the outbreak was halted , so it wasn ’ t as if it magically stopped after 30 % of people got the virus , Andersen says .
“ There ’ s no mysterious dark matter that protects people , ” he says .
And although scientists can estimate herd-immunity thresholds , they won ’ t know the actual numbers in real @ @ @ @ @ @ @ epidemiologist at the Johns Hopkins Center for Health Security in Baltimore .
Instead , herd immunity is something that can be observed with certainty only by analysing the data in retrospect , maybe as long as ten years afterwards , she says .
Many researchers say pursuing herd immunity is a bad idea .
“ Attempting to reach herd immunity via targeted infections is simply ludicrous , ” Andersen says .
“ In the US , probably one to two million people would die.
” In Manaus , mortality rates during the first @ @ @ @ @ @ @ what they had been the preceding year .
And despite the subsequent excitement over the August slowdown in cases , numbers seem to be rising again .
This surge shows that speculation that the population in Manaus has reached herd immunity “ just isn ’ t true ” , Andersen says .
Deaths are only one part of the equation .
Individuals who become ill with the disease can experience serious medical and financial consequences , and many people who have recovered from the virus report lingering health effects .
More than 58,000 @ @ @ @ @ @ @ , so that translates to a lot of human suffering .
Earlier in the pandemic , media reports claimed that Sweden was pursuing a herd immunity strategy by essentially letting people live their lives as normal , but that idea is a “ misunderstanding ” , according to the country ’ s minister for health and social affairs , Lena Hallengren .
Herd immunity “ is a potential consequence of how the spread of the virus develops , in Sweden or in any other country ” , she told Nature in a written @ @ @ @ @ @ @ a part of our strategy ” .
Sweden ’ s approach , she said , uses similar tools to most other countries : “ Promoting social distancing , protecting vulnerable people , carrying out testing and contact tracing , and reinforcing our health system to cope with the pandemic.
” Despite this , Sweden is hardly a model of success—statistics from Johns Hopkins University show the country has seen more than ten times the number of COVID-19 deaths per 100,000 people seen in neighbouring Norway ( 58.12 per 100,000 , compared with 5.23 @ @ @ @ @ @ @ ’ s case fatality rate , which is based on the number of known infections , is also at least three times those of Norway and nearby Denmark .
What else stands in the way of herd immunity ?
The concept of achieving herd immunity through community spread of a pathogen rests on the unproven assumption that people who survive an infection will become immune .
For SARS-CoV-2 , some kind of functional immunity seems to follow infection , but “ to understand the duration and effects of the immune response we have @ @ @ @ @ @ @ ’ s still early days ” , Buckee says .
Nor is there yet a foolproof way to measure immunity to the virus , Rivers says .
Researchers can test whether people have antibodies that are specific to SARS-CoV-2 , but they still don ’ t know how long any immunity might last .
Seasonal coronaviruses that cause common colds provoke a waning immunity that seems to last approximately a year , Buckee says .
“ It seems reasonable as a hypothesis to assume this one will be similar.
” In recent months @ @ @ @ @ @ @ being reinfected with SARS-CoV-2 after an initial infection , but how frequently these reinfections happen and whether they result in less serious illnesses remain open questions , says Andersen .
“ If the people who are infected become susceptible again in a year , then basically you ’ ll never reach herd immunity ” through natural transmission , Rivers says .
“ There ’ s no magic wand we can use here , ” Andersen says .
“ We have to face reality—never before have we reached herd immunity via natural infection with @ @ @ @ @ @ @ unfortunately no different.
” Vaccination is the only ethical path to herd immunity , he says .
How many people will need to be vaccinated—and how often—will depend on many factors , including how effective the vaccine is and how long its protection lasts .
People are understandably tired and frustrated with imposed measures such as social distancing and shutdowns to control the spread of COVID-19 , but until there is a vaccine , these are some of the best tools around .
“ It is not inevitable that we all have to @ @ @ @ @ @ @ Souza says .
“ There are a lot of reasons to be very hopeful .
If we can continue risk-mitigation approaches until we have an effective vaccine , we can absolutely save lives.
” This article is reproduced with permission and was first published on October 21 2020 .

In May, the Brazilian city of Manaus was devastated by a large outbreak of COVID-19. Hospitals were overwhelmed and the city was digging new grave sites in the surrounding forest. But by August, something had shifted. Despite relaxing social-distancing requirements in early June, the city of 2 million people had reduced its number of excess deaths from around 120 per day to nearly zero.
In September, two groups of researchers posted preprints suggesting that Manaus’s late-summer slowdown in COVID-19 cases had happened, at least in part, because a large proportion of the community’s population had already been exposed to the virus and was now immune. Immunologist Ester Sabino at the University of São Paulo, Brazil, and her colleagues tested more than 6,000 samples from blood banks in Manaus for antibodies to SARS-CoV-2.
“We show that the number of people who got infected was really high—reaching 66% by the end of the first wave,” Sabino says. Her group concluded that this large infection rate meant that the number of people who were still vulnerable to the virus was too small to sustain new outbreaks—a phenomenon called herd immunity. Another group in Brazil reached similar conclusions.
Such reports from Manaus, together with comparable arguments about parts of Italy that were hit hard early in the pandemic, helped to embolden proposals to chase herd immunity. The plans suggested letting most of society return to normal, while taking some steps to protect those who are most at risk of severe disease. That would essentially allow the coronavirus to run its course, proponents said.
But epidemiologists have repeatedly smacked down such ideas. “Surrendering to the virus” is not a defensible plan, says Kristian Andersen, an immunologist at the Scripps Research Institute in La Jolla, California. Such an approach would lead to a catastrophic loss of human lives without necessarily speeding up society’s return to normal, he says. “We have never successfully been able to do it before, and it will lead to unacceptable and unnecessary untold human death and suffering.”
Despite widespread critique, the idea keeps popping up among politicians and policymakers in numerous countries, including Sweden, the United Kingdom and the United States. US President Donald Trump spoke positively about it in September, using the malapropism “herd mentality”. And even a few scientists have pushed the agenda. In early October, a libertarian think tank and a small group of scientists released a document called the Great Barrington Declaration. In it, they call for a return to normal life for people at lower risk of severe COVID-19, to allow SARS-CoV-2 to spread to a sufficient level to give herd immunity. People at high risk, such as elderly people, it says, could be protected through measures that are largely unspecified. The writers of the declaration received an audience in the White House, and sparked a counter memorandum from another group of scientists in The Lancet, which called the herd-immunity approach a “dangerous fallacy unsupported by scientific evidence”.
Arguments in favour of allowing the virus to run its course largely unchecked share a misunderstanding about what herd immunity is, and how best to achieve it. Here, Nature answers five questions about the controversial idea.
What is herd immunity?
Herd immunity happens when a virus can’t spread because it keeps encountering people who are protected against infection. Once a sufficient proportion of the population is no longer susceptible, any new outbreak peters out. “You don’t need everyone in the population to be immune—you just need enough people to be immune,” says Caroline Buckee, an epidemiologist at Harvard T.H. Chan School of Public Health in Boston, Massachusetts.
Typically, herd immunity is discussed as a desirable result of wide-scale vaccination programmes. High levels of vaccination-induced immunity in the population benefits those who can’t receive or sufficiently respond to a vaccine, such as people with compromised immune systems. Many medical professionals hate the term herd immunity, and prefer to call it “herd protection”, Buckee says. That’s because the phenomenon doesn’t actually confer immunity to the virus itself—it only reduces the risk that vulnerable people will come into contact with the pathogen.
But public-health experts don’t usually talk about herd immunity as a tool in the absence of vaccines. “I’m a bit puzzled that it’s now used to mean how many people need to get infected before this thing stops,” says Marcel Salathé, an epidemiologist at the Swiss Federal Institute of Technology in Lausanne.
How do you achieve it?
Epidemiologists can estimate the proportion of a population that needs to be immune before herd immunity kicks in. This threshold depends on the basic reproduction number, R0—the number of cases, on average, spawned by one infected individual in an otherwise fully susceptible, well-mixed population, says Kin On Kwok, an infectious-disease epidemiologist and mathematical modeller at the Chinese University of Hong Kong. The formula for calculating the herd-immunity threshold is 1–1/R0—meaning that the more people who become infected by each individual who has the virus, the higher the proportion of the population that needs to be immune to reach herd immunity. For instance, measles is extremely infectious, with an R0 typically between 12 and 18, which works out to a herd-immunity threshold of 92–94% of the population. For a virus that is less infectious (with a lower reproduction number), the threshold would be lower. The R0 assumes that everyone is susceptible to the virus, but that changes as the epidemic proceeds, because some people become infected and gain immunity. For that reason, a variation of R0 called the R effective (abbreviated Rt or Re) is sometimes used in these calculations, because it takes into consideration changes in susceptibility in the population.
Although plugging numbers into the formula spits out a theoretical number for herd immunity, in reality, it isn’t achieved at an exact point. Instead, it’s better to think of it as a gradient, says Gypsyamber D’Souza, an epidemiologist at Johns Hopkins University in Baltimore, Maryland. And because variables can change, including R0 and the number of people susceptible to a virus, herd immunity is not a steady state.
Even once herd immunity is attained across a population, it’s still possible to have large outbreaks, such as in areas where vaccination rates are low. “We’ve seen that play out in certain countries where misinformation about vaccine safety has spread,” Salathé says. “In local pockets, you start to see a drop in vaccinations, and then you can have local outbreaks which can be very large, even though you’ve technically reached herd immunity as per the math.” The ultimate goal is to prevent people from becoming unwell, rather than to attain a number in a model.
How high is the threshold for SARS-CoV-2?
Reaching herd immunity depends in part on what’s happening in the population. Calculations of the threshold are very sensitive to the values of R, Kwok says. In June, he and his colleagues published a letter to the editor in the Journal of Infection that demonstrates this. Kwok and his team estimated the Rt in more than 30 countries, using data on the daily number of new COVID-19 cases from March. They then used these values to calculate a threshold for herd immunity in each country’s population. The numbers ranged from as high as 85% in Bahrain, with its then-Rt of 6.64, to as low as 5.66% in Kuwait, where the Rt was 1.06. Kuwait’s low numbers reflected the fact that it was putting in place lots of measures to control the virus, such as establishing local curfews and banning commercial flights from many countries. If the country stopped those measures, Kwok says, the herd-immunity threshold would go up.
Herd-immunity calculations such as the ones in Kwok’s example are built on assumptions that might not reflect real life, says Samuel Scarpino, a network scientist who studies infectious disease at Northeastern University in Boston, Massachusetts. “Most of the herd-immunity calculations don’t have anything to say about behaviour at all. They assume there’s no interventions, no behavioural changes or anything like that,” he says. This means that if a transient change in people’s behaviour (such as physical distancing) drives the Rt down, then “as soon as that behaviour goes back to normal, the herd-immunity threshold will change.”
Estimates of the threshold for SARS-CoV-2 range from 10% to 70% or even more. But models that calculate numbers at the lower end of that range rely on assumptions about how people interact in social networks that might not hold true, Scarpino says. Low-end estimates imagine that people with many contacts will get infected first, and that because they have a large number of contacts, they will spread the virus to more people. As these ‘superspreaders’ gain immunity to the virus, the transmission chains among those who are still susceptible are greatly reduced. And “as a result of that, you very quickly get to the herd-immunity threshold”, Scarpino says. But if it turns out that anybody could become a superspreader, then “those assumptions that people are relying on to get the estimates down to around 20% or 30% are just not accurate”, Scarpino explains. The result is that the herd-immunity threshold will be closer to 60–70%, which is what most models show (see, for example, ref. 6).
Looking at known superspreader events in prisons and on cruise ships, it seems clear that COVID-19 spreads widely initially, before slowing down in a captive, unvaccinated population, Andersen says. At San Quentin State Prison in California, more than 60% of the population was ultimately infected before the outbreak was halted, so it wasn’t as if it magically stopped after 30% of people got the virus, Andersen says. “There’s no mysterious dark matter that protects people,” he says.
And although scientists can estimate herd-immunity thresholds, they won’t know the actual numbers in real time, says Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security in Baltimore. Instead, herd immunity is something that can be observed with certainty only by analysing the data in retrospect, maybe as long as ten years afterwards, she says.
Will herd immunity work?
Many researchers say pursuing herd immunity is a bad idea. “Attempting to reach herd immunity via targeted infections is simply ludicrous,” Andersen says. “In the US, probably one to two million people would die.”
In Manaus, mortality rates during the first week of May soared to four-and-a-half times what they had been the preceding year. And despite the subsequent excitement over the August slowdown in cases, numbers seem to be rising again. This surge shows that speculation that the population in Manaus has reached herd immunity “just isn’t true”, Andersen says.
Deaths are only one part of the equation. Individuals who become ill with the disease can experience serious medical and financial consequences, and many people who have recovered from the virus report lingering health effects. More than 58,000 people were infected with SARS-CoV-2 in Manaus, so that translates to a lot of human suffering.
Earlier in the pandemic, media reports claimed that Sweden was pursuing a herd immunity strategy by essentially letting people live their lives as normal, but that idea is a “misunderstanding”, according to the country’s minister for health and social affairs, Lena Hallengren. Herd immunity “is a potential consequence of how the spread of the virus develops, in Sweden or in any other country”, she told Nature in a written statement, but it is “not a part of our strategy”. Sweden’s approach, she said, uses similar tools to most other countries: “Promoting social distancing, protecting vulnerable people, carrying out testing and contact tracing, and reinforcing our health system to cope with the pandemic.” Despite this, Sweden is hardly a model of success—statistics from Johns Hopkins University show the country has seen more than ten times the number of COVID-19 deaths per 100,000 people seen in neighbouring Norway (58.12 per 100,000, compared with 5.23 per 100,000 in Norway). Sweden’s case fatality rate, which is based on the number of known infections, is also at least three times those of Norway and nearby Denmark.
What else stands in the way of herd immunity?
The concept of achieving herd immunity through community spread of a pathogen rests on the unproven assumption that people who survive an infection will become immune. For SARS-CoV-2, some kind of functional immunity seems to follow infection, but “to understand the duration and effects of the immune response we have to follow people longitudinally, and it’s still early days”, Buckee says.
Nor is there yet a foolproof way to measure immunity to the virus, Rivers says. Researchers can test whether people have antibodies that are specific to SARS-CoV-2, but they still don’t know how long any immunity might last. Seasonal coronaviruses that cause common colds provoke a waning immunity that seems to last approximately a year, Buckee says. “It seems reasonable as a hypothesis to assume this one will be similar.”
In recent months, there have been reports of people being reinfected with SARS-CoV-2 after an initial infection, but how frequently these reinfections happen and whether they result in less serious illnesses remain open questions, says Andersen. “If the people who are infected become susceptible again in a year, then basically you’ll never reach herd immunity” through natural transmission, Rivers says.
“There’s no magic wand we can use here,” Andersen says. “We have to face reality—never before have we reached herd immunity via natural infection with a novel virus, and SARS-CoV-2 is unfortunately no different.” Vaccination is the only ethical path to herd immunity, he says. How many people will need to be vaccinated—and how often—will depend on many factors, including how effective the vaccine is and how long its protection lasts.
People are understandably tired and frustrated with imposed measures such as social distancing and shutdowns to control the spread of COVID-19, but until there is a vaccine, these are some of the best tools around. “It is not inevitable that we all have to get this infection,” D’Souza says. “There are a lot of reasons to be very hopeful. If we can continue risk-mitigation approaches until we have an effective vaccine, we can absolutely save lives.”
This article is reproduced with permission and was first published on October 21 2020.


scientificamerican--2020-10-24--COVID's Other Toll: Unnecessary Tests and Huge Hospital Bills

In a physician chat group recently , a doctor who treats hospitalized patients made a recommendation to our group of 38,000 members that left me startled and alarmed .
She shared her protocol for all COVID-19 patients admitted to the hospital : every one of them gets not only a chest x-ray but an entire battery of special tests , including a coagulation test , a leg ultrasound and a CT scan .
This was offered as her blanket standard of care .
What it actually represents to me is one of the biggest problems with health care in America—because @ @ @ @ @ @ @ tests .
And this is not a new story .
Simply put , as physicians in the U.S. , we overdiagnose and overtreat people .
We order way too many tests , treatments and surgeries that you don ’ t need and that may actually harm you—and they cost money , lots of it .
Incredibly , in a nation of 328 million people , we order approximately 15 million nuclear imaging studies , 100 million MRIs and CT scans and close to 10 billion blood tests on patients every year .
We @ @ @ @ @ @ @ pinch of “ err on the side of caution ” here .
We are talking about runaway medicine , with patients aboard a system with no brakes , few guardrails and no one fully at the controls .
Moreover , we as physicians don ’ t do a good job informing you of the downstream risk of these costly procedures , because we may not even recognize the mess we are creating in the first place .
Why all the tests ?
Well , we may order them because we are worried about @ @ @ @ @ @ @ get you healthy as soon as possible .
Sometimes , it is to avoid getting sued .
( When in doubt , it ’ s always easier to test . )
Sometimes it ’ s because patients request the tests and we yield .
Less innocently , we may order more tests because they bring in more money .
We are doctors , but we are revenue generators too , and , for some , not necessarily in that order .
Let me walk you through two overdiagnosis/testing hypotheticals .
Here ’ s @ @ @ @ @ @ @ hospital with a cough and a low-grade fever .
You test positive for COVID-19 , and a chest x-ray demonstrates that you have a pneumonia .
This is a fairly typical scenario .
As a clinician , though , I also opt for a CT scan to make sure you do not have a blood clot in the lung ( a pulmonary embolism ) , even though when you were admitted most doctors already would have put you on a prophylactic lower dose of a blood-thinner for this—to help prevent clotting .
The @ @ @ @ @ @ @ we knew that already from the x-ray .
There is no finding of a pulmonary embolism .
But the scan it does show a little something of which I ’ m not exactly sure—a possible nodule , or what we physicians refer to as an “ incidentaloma.
” This is not uncommon ; incidental solitary lung nodules are found on CT studies from 8 to 51 percent of the time .
Per an expert panel of the American College of Radiology , most incidentalomas found on imaging studies are benign .
In fact @ @ @ @ @ @ @ on chest CT are benign—that is , not cancerous .
But their discovery can lead to extensive downstream testing , worry and potential morbidity , as we doctors start poking and prodding you , wanting to assure ourselves that the incidentaloma is indeed nothing .
I inform you of the nodule in your lung .
You pepper me with questions and become worried , because , after all , sometimes nodules are cancerous .
We may run more tests to assess it , but more likely we ’ ll monitor this nodule for @ @ @ @ @ @ @ at various intervals to see whether it changes in size .
These tests will expose you to additional radiation , which may increase your risk of cancer years down the road , and cost you money .
If we are more concerned about your incidentaloma , we may decide to do a lung biopsy , in which we stick a needle directly into the lung to get a tissue sample for evaluation .
Not very often , but occasionally , we accidentally poke a hole in the lung , causing what is called @ @ @ @ @ @ @ and can make you immediately short of breath or sometimes even cause a drop in your blood pressure .
Now , not only have you received potentially dangerous radiation from the original CT scan , but you have undergone an invasive procedure and you ’ ve experienced harm .
This particular complication will likely require the placement of a chest tube or a Thora-Vent device , both of which are invasive and can be very painful .
If the pneumothorax is significant , it will mean a hospital stay in order to observe @ @ @ @ @ @ @ , is that we never needed to go down this path— but here we are .
Here ’ s another scenario , and one that is much more common .
Instead of the incidentaloma , we find a small pulmonary embolism ( PE ) .
As your doctor , I breathe a sigh of relief and pat myself on the back for ordering a test that I didn ’ t really think you needed , but one that yielded this discovery .
But here ’ s the catch : From the time CT @ @ @ @ @ @ @ years ago , we have dramatically increased the number of patients in whom we look for and diagnose PE .
“ There is good reason to believe that this hasn ’ t done anything good , ” says Jerome Hoffman , professor emeritus at UCLA Medical Center and an expert on overdiagnosis .
In an interview , Hoffman told me that doctors used to look for PEs “ only when patients were clinically very ill , '' and the PEs they found were indeed very important ; they killed about one in five @ @ @ @ @ @ @ .
Now , “ because it is so easy to look with CT , we find a lot more PEs , but the same number of patients die—meaning that your chance of dying from a PE today is drastically less.
” Hoffman calls the lower case-fatality rate an optical illusion , in that we ’ re now finding so many more PEs , the vast majority of which would be clinically insignificant .
In our hypothetical , though , we don ’ t have evidence from randomized controlled trials to conclude that ignoring @ @ @ @ @ @ @ I feel compelled to treat you .
Treatment is controversial : some guidelines suggest it ’ s not required , some advise to consider it on a case-by-case basis , and others recommend treating most cases .
I choose to prescribe you a blood thinner medication—but sometimes this has harmful side effects , like serious bleeding .
This might lead to you needing blood transfusions , which , of course , carry their own risk .
You ’ re now transferred to the intensive care unit .
And so it goes .
Technology @ @ @ @ @ @ @ the solution .
And , says Hoffman , “ This will only get worse as our wondrous technology ‘ improves , ’ and we find ever tinier abnormalities that we otherwise wouldn ’ t have known existed , and wouldn ’ t have caused any harm.
” The cost is staggering .
At least 30,000 deaths in the U.S. each year are linked to mistakes and injuries caused by superfluous medical treatment .
Meanwhile , unnecessary testing and surgeries add up to more than $ 200 billion in extra spending per year in @ @ @ @ @ @ @ of Medicine .
In a 2017 survey , doctors from the American Medical Association ( AMA ) said that nearly a quarter of all the tests they performed were unnecessary , along with more than 20 percent of the prescriptions they wrote and every 10th surgery .
Researchers estimate that among cancers detected by screening , some 11–19 percent of breast cancers and 20–50 percent of prostate cancers constitute overdiagnosis .
Too much medical care is a true public health crisis in this country .
But such treatments continue to be pushed as @ @ @ @ @ @ @ 3.8 trillion domestic health care market—and hospitals , insurers , device makers and big pharma are scooping up the profits .
Let ’ s get back to your COVID-19 admission .
What ’ s that going to wind up costing you ?
FAIR Health analyzed data from over 30 billion private health care claim records , using revenue codes associated with influenza and pneumonia as a means of estimating these costs .
Their finding : The average charge for a hospitalized COVID-19 patient stay would be $ 73,300 if the patient were either @ @ @ @ @ @ @ That estimate is significantly lower for a privately insured patient with an in-network provider , but it still clocks in at a breathtaking $ 38,221 .
( How much you ’ d actually pay , of course , depends on your health plan deductible and the cost-sharing policies of your insurer . )
Throw in some extra testing charges , and it ’ s little wonder that nearly one third of working Americans have some level of medical debt , with 28 percent of those owing at least $ 10,000 .
As physicians @ @ @ @ @ @ @ help patients , not bankrupt them .
But medicine has become a business replete with overdiagnosis and overtreatment—and skyrocketing medical charges .
It ’ s clear that our health care system needs significant reform .
A broader discussion of that change is beyond the scope of this article , but here are some ideas to kick-start the process .
First , rein in hospital and pharmaceutical price gouging via market forces , price caps or regulation .
Use value-based or bundled care , rather than fee-for-service medicine , to reduce the impetus to @ @ @ @ @ @ @ to help alleviate the practice of defensive medicine .
Push for cost transparency so that prices are knowable to patients ahead of time , thus allowing for informed decisions .
Eliminate some of the enormous administrative excesses and various middlemen who siphon off profits in our medical supply chain , spiking costs .
You should absolutely see a physician for your health concerns , especially if you are sick with COVID-19 ; it ’ s a dangerous virus .
But don ’ t ever be afraid to speak up and ask why tests @ @ @ @ @ @ @ are being consulted , why procedures or surgeries are being scheduled , or why you are being admitted .
If it ’ s an elective situation , feel free to get a second or third opinion .
Let ’ s take our health back while keeping our wallets intact .
As we ’ ve seen repeatedly , it is often true in medicine that less is more .

In a physician chat group recently, a doctor who treats hospitalized patients made a recommendation to our group of 38,000 members that left me startled and alarmed. She shared her protocol for all COVID-19 patients admitted to the hospital: every one of them gets not only a chest x-ray but an entire battery of special tests, including a coagulation test, a leg ultrasound and a CT scan.
This was offered as her blanket standard of care. What it actually represents to me is one of the biggest problems with health care in America—because not every admitted patient needs all these tests. And this is not a new story.
Simply put, as physicians in the U.S., we overdiagnose and overtreat people. We order way too many tests, treatments and surgeries that you don’t need and that may actually harm you—and they cost money, lots of it. Incredibly, in a nation of 328 million people, we order approximately 15 million nuclear imaging studies, 100 million MRIs and CT scans and close to 10 billion blood tests on patients every year.
We’re not talking about a little pinch of “err on the side of caution” here. We are talking about runaway medicine, with patients aboard a system with no brakes, few guardrails and no one fully at the controls. Moreover, we as physicians don’t do a good job informing you of the downstream risk of these costly procedures, because we may not even recognize the mess we are creating in the first place.
Why all the tests? Well, we may order them because we are worried about missing a diagnosis and we want to get you healthy as soon as possible. Sometimes, it is to avoid getting sued. (When in doubt, it’s always easier to test.) Sometimes it’s because patients request the tests and we yield. Less innocently, we may order more tests because they bring in more money. We are doctors, but we are revenue generators too, and, for some, not necessarily in that order.
Let me walk you through two overdiagnosis/testing hypotheticals. Here’s one: You are admitted to the hospital with a cough and a low-grade fever. You test positive for COVID-19, and a chest x-ray demonstrates that you have a pneumonia. This is a fairly typical scenario. As a clinician, though, I also opt for a CT scan to make sure you do not have a blood clot in the lung (a pulmonary embolism), even though when you were admitted most doctors already would have put you on a prophylactic lower dose of a blood-thinner for this—to help prevent clotting.
The CT scan again shows the pneumonia; we knew that already from the x-ray. There is no finding of a pulmonary embolism. But the scan it does show a little something of which I’m not exactly sure—a possible nodule, or what we physicians refer to as an “incidentaloma.” This is not uncommon; incidental solitary lung nodules are found on CT studies from 8 to 51 percent of the time. Per an expert panel of the American College of Radiology, most incidentalomas found on imaging studies are benign. In fact, 99 percent of lung nodules found on chest CT are benign—that is, not cancerous. But their discovery can lead to extensive downstream testing, worry and potential morbidity, as we doctors start poking and prodding you, wanting to assure ourselves that the incidentaloma is indeed nothing.
I inform you of the nodule in your lung. You pepper me with questions and become worried, because, after all, sometimes nodules are cancerous. We may run more tests to assess it, but more likely we’ll monitor this nodule for months—years, sometimes—and do additional CT scans at various intervals to see whether it changes in size. These tests will expose you to additional radiation, which may increase your risk of cancer years down the road, and cost you money.
If we are more concerned about your incidentaloma, we may decide to do a lung biopsy, in which we stick a needle directly into the lung to get a tissue sample for evaluation. Not very often, but occasionally, we accidentally poke a hole in the lung, causing what is called a pneumothorax. This is quite serious and can make you immediately short of breath or sometimes even cause a drop in your blood pressure.
Now, not only have you received potentially dangerous radiation from the original CT scan, but you have undergone an invasive procedure and you’ve experienced harm. This particular complication will likely require the placement of a chest tube or a Thora-Vent device, both of which are invasive and can be very painful. If the pneumothorax is significant, it will mean a hospital stay in order to observe you. Key here, of course, is that we never needed to go down this path— but here we are.
Here’s another scenario, and one that is much more common. Instead of the incidentaloma, we find a small pulmonary embolism (PE). As your doctor, I breathe a sigh of relief and pat myself on the back for ordering a test that I didn’t really think you needed, but one that yielded this discovery.
But here’s the catch: From the time CT pulmonary angiography was first used about 30 years ago, we have dramatically increased the number of patients in whom we look for and diagnose PE. “There is good reason to believe that this hasn’t done anything good,” says Jerome Hoffman, professor emeritus at UCLA Medical Center and an expert on overdiagnosis.
In an interview, Hoffman told me that doctors used to look for PEs “only when patients were clinically very ill," and the PEs they found were indeed very important; they killed about one in five people with this diagnosis, he says. Now, “because it is so easy to look with CT, we find a lot more PEs, but the same number of patients die—meaning that your chance of dying from a PE today is drastically less.” Hoffman calls the lower case-fatality rate an optical illusion, in that we’re now finding so many more PEs, the vast majority of which would be clinically insignificant.
In our hypothetical, though, we don’t have evidence from randomized controlled trials to conclude that ignoring these small clots is safe, so I feel compelled to treat you. Treatment is controversial: some guidelines suggest it’s not required, some advise to consider it on a case-by-case basis, and others recommend treating most cases. I choose to prescribe you a blood thinner medication—but sometimes this has harmful side effects, like serious bleeding. This might lead to you needing blood transfusions, which, of course, carry their own risk. You’re now transferred to the intensive care unit. And so it goes.
Technology becomes the problem rather than part of the solution. And, says Hoffman, “This will only get worse as our wondrous technology ‘improves,’ and we find ever tinier abnormalities that we otherwise wouldn’t have known existed, and wouldn’t have caused any harm.”
The cost is staggering. At least 30,000 deaths in the U.S. each year are linked to mistakes and injuries caused by superfluous medical treatment. Meanwhile, unnecessary testing and surgeries add up to more than $200 billion in extra spending per year in the U.S., according to the Institute of Medicine.
In a 2017 survey, doctors from the American Medical Association (AMA) said that nearly a quarter of all the tests they performed were unnecessary, along with more than 20 percent of the prescriptions they wrote and every 10th surgery. Researchers estimate that among cancers detected by screening, some 11–19 percent of breast cancers and 20–50 percent of prostate cancers constitute overdiagnosis.
Too much medical care is a true public health crisis in this country. But such treatments continue to be pushed as part of what is already a $3.8 trillion domestic health care market—and hospitals, insurers, device makers and big pharma are scooping up the profits.
Let’s get back to your COVID-19 admission. What’s that going to wind up costing you? FAIR Health analyzed data from over 30 billion private health care claim records, using revenue codes associated with influenza and pneumonia as a means of estimating these costs. Their finding: The average charge for a hospitalized COVID-19 patient stay would be $73,300 if the patient were either uninsured or seeing an out-of-network provider.
That estimate is significantly lower for a privately insured patient with an in-network provider, but it still clocks in at a breathtaking $38,221. (How much you’d actually pay, of course, depends on your health plan deductible and the cost-sharing policies of your insurer.) Throw in some extra testing charges, and it’s little wonder that nearly one third of working Americans have some level of medical debt, with 28 percent of those owing at least $10,000.
As physicians, we all went into medicine to help patients, not bankrupt them. But medicine has become a business replete with overdiagnosis and overtreatment—and skyrocketing medical charges. It’s clear that our health care system needs significant reform.
A broader discussion of that change is beyond the scope of this article, but here are some ideas to kick-start the process. First, rein in hospital and pharmaceutical price gouging via market forces, price caps or regulation. Use value-based or bundled care, rather than fee-for-service medicine, to reduce the impetus to order more. Initiate tort reform, to help alleviate the practice of defensive medicine. Push for cost transparency so that prices are knowable to patients ahead of time, thus allowing for informed decisions. Eliminate some of the enormous administrative excesses and various middlemen who siphon off profits in our medical supply chain, spiking costs.
You should absolutely see a physician for your health concerns, especially if you are sick with COVID-19; it’s a dangerous virus. But don’t ever be afraid to speak up and ask why tests are being ordered. Ask why specialists are being consulted, why procedures or surgeries are being scheduled, or why you are being admitted. If it’s an elective situation, feel free to get a second or third opinion.
Let’s take our health back while keeping our wallets intact. As we’ve seen repeatedly, it is often true in medicine that less is more.


scientificamerican--2020-10-25--Why COVID Outbreaks Could Worsen This Winter

Winter is fast approaching in the Northern Hemisphere , and researchers warn that COVID-19 outbreaks are likely to get worse , especially in regions that don ’ t have the virus ’ s spread under control .
“ This virus is going to have a heyday , ” says David Relman , a microbiologist at Stanford University in California .
“ We are looking at some pretty sobering and difficult months ahead.
” Infections caused by many respiratory viruses , including influenza and some coronaviruses , swell in winter and drop in summer .
Researchers say it ’ s too @ @ @ @ @ @ @ whether SARS-CoV-2 will become a seasonal virus .
But growing evidence suggests that a small seasonal effect will probably contribute to bigger outbreaks in winter , on the basis of what is known about how the virus spreads and how people behave in colder months .
People will be interacting more often indoors in places with poor ventilation , which will increase the risk of transmission , says Mauricio Santillana , a mathematician at Harvard Medical School in Boston , Massachusetts , who models disease spread .
But even if there is a @ @ @ @ @ @ @ of increased spread will be the vast number of people who are still susceptible to infection , says Rachel Baker , an epidemiologist at Princeton University in New Jersey .
That means people in places that are going into summer shouldn ’ t be complacent either , say researchers .
“ By far the biggest factor that will affect the size of an outbreak will be control measures such as social distancing and mask wearing , ” says Baker .
Seasonal trends in viral infection are driven by multiple factors , including people @ @ @ @ @ @ @ the virus—some don ’ t like hot , humid conditions .
Laboratory experiments reveal that SARS-CoV-2 favours cold , dry conditions , particularly out of direct sunlight .
For instance , artificial ultraviolet radiation can inactivate SARS-CoV-2 particles on surfaces and in aerosols , especially in temperatures of around 40 °C .
Infectious virus also degrades faster on surfaces in warmer and more humid environments .
In winter , people tend to heat their houses to around 20 °C , and the air is dry and not well ventilated , says Dylan Morris @ @ @ @ @ @ @ “ Indoor conditions in the winter are pretty favourable to viral stability.
” To assess whether infections with a particular virus rise and fall with the seasons , researchers typically study its spread in a specific location , multiple times a year , over many years .
But without the benefit of time , they have tried to study the seasonal contribution to SARS-CoV-2 transmission by looking at infection rates in various places worldwide .
A study published on 13 October looked at the growth in SARS-CoV-2 infections in the first four months @ @ @ @ @ @ @ introduced controls .
It found that infections rose fastest in places with less UV light , and predicted that , without any interventions , cases would dip in summer and peak in winter .
In winter , “ the risk goes up , but you can still dramatically reduce your risk by good personal behaviour ” , says Cory Merow , an ecologist at the University of Connecticut in Storrs , and a co-author of the study .
“ The weather is a small drop in the pan.
” But Francois Cohen , @ @ @ @ @ @ @ Barcelona in Spain , says that testing was also quite limited early in the pandemic , and continues to be unreliable , so it is impossible to determine the effect of weather on the spread of the virus so far .
Baker has tried to tease apart the effect of climate on the seasonal pattern of cases during the course of a pandemic , using data about the humidity sensitivity of another coronavirus .
She and her colleagues modelled the rise and fall in infection rates over several years for New York City @ @ @ @ @ @ @ and with different levels of control measures .
They found that a small climate effect can result in substantial outbreaks when the seasons change if control measures are only just managing to contain the virus .
“ That could be a location where climate might nudge you over , ” Baker says .
The team posted its results on the preprint server medRxiv on 10 September ; the authors suggest that stricter control measures might be needed during winter to reduce the risk of outbreaks .
If SARS-CoV-2 can survive better in cold @ @ @ @ @ @ @ to disentangle that contribution from the effect of people ’ s behaviour , says Kathleen O ’ Reilly , a mathematical epidemiologist at the London School of Hygiene and Tropical Medicine .
“ Flu has been around for hundreds of years and the specific mechanism as to why you have peaks of flu in the winter is still poorly understood , ” says O ’ Reilly .
And even if researchers had more reliable data for SARS-CoV-2 , they would see only small or negligible seasonal effects so early in the pandemic , @ @ @ @ @ @ @ susceptible , says Relman .
Over time , however , seasonal effects could play a more important part in driving infection trends , as more people build up immunity to the virus .
This could take up to five years through natural infection , or less if people are vaccinated , says Baker .
But whether a seasonal pattern emerges at all , and what it will look like , will depend on many factors that are yet to be understood , including how long immunity lasts , how long recovery takes and @ @ @ @ @ @ @ be reinfected , says Colin Carlson , a biologist who studies emerging diseases at Georgetown University in Washington DC .
This article is reproduced with permission and was first published on October 23 2020 .

Winter is fast approaching in the Northern Hemisphere, and researchers warn that COVID-19 outbreaks are likely to get worse, especially in regions that don’t have the virus’s spread under control.
“This virus is going to have a heyday,” says David Relman, a microbiologist at Stanford University in California. “We are looking at some pretty sobering and difficult months ahead.”
Infections caused by many respiratory viruses, including influenza and some coronaviruses, swell in winter and drop in summer. Researchers say it’s too early in the COVID-19 pandemic to say whether SARS-CoV-2 will become a seasonal virus. But growing evidence suggests that a small seasonal effect will probably contribute to bigger outbreaks in winter, on the basis of what is known about how the virus spreads and how people behave in colder months.
People will be interacting more often indoors in places with poor ventilation, which will increase the risk of transmission, says Mauricio Santillana, a mathematician at Harvard Medical School in Boston, Massachusetts, who models disease spread.
But even if there is a small seasonal effect, the main driver of increased spread will be the vast number of people who are still susceptible to infection, says Rachel Baker, an epidemiologist at Princeton University in New Jersey. That means people in places that are going into summer shouldn’t be complacent either, say researchers.
“By far the biggest factor that will affect the size of an outbreak will be control measures such as social distancing and mask wearing,” says Baker.
Evidence so far
Seasonal trends in viral infection are driven by multiple factors, including people’s behaviour and the properties of the virus—some don’t like hot, humid conditions.
Laboratory experiments reveal that SARS-CoV-2 favours cold, dry conditions, particularly out of direct sunlight. For instance, artificial ultraviolet radiation can inactivate SARS-CoV-2 particles on surfaces and in aerosols, especially in temperatures of around 40 °C. Infectious virus also degrades faster on surfaces in warmer and more humid environments. In winter, people tend to heat their houses to around 20 °C, and the air is dry and not well ventilated, says Dylan Morris, a mathematical biologist at Princeton. “Indoor conditions in the winter are pretty favourable to viral stability.”
To assess whether infections with a particular virus rise and fall with the seasons, researchers typically study its spread in a specific location, multiple times a year, over many years. But without the benefit of time, they have tried to study the seasonal contribution to SARS-CoV-2 transmission by looking at infection rates in various places worldwide.
A study published on 13 October looked at the growth in SARS-CoV-2 infections in the first four months of the pandemic, before most countries introduced controls. It found that infections rose fastest in places with less UV light, and predicted that, without any interventions, cases would dip in summer and peak in winter. In winter, “the risk goes up, but you can still dramatically reduce your risk by good personal behaviour”, says Cory Merow, an ecologist at the University of Connecticut in Storrs, and a co-author of the study. “The weather is a small drop in the pan.”
But Francois Cohen, an environmental economist at the University of Barcelona in Spain, says that testing was also quite limited early in the pandemic, and continues to be unreliable, so it is impossible to determine the effect of weather on the spread of the virus so far.
Baker has tried to tease apart the effect of climate on the seasonal pattern of cases during the course of a pandemic, using data about the humidity sensitivity of another coronavirus. She and her colleagues modelled the rise and fall in infection rates over several years for New York City with and without a climate effect, and with different levels of control measures. They found that a small climate effect can result in substantial outbreaks when the seasons change if control measures are only just managing to contain the virus. “That could be a location where climate might nudge you over,” Baker says. The team posted its results on the preprint server medRxiv on 10 September; the authors suggest that stricter control measures might be needed during winter to reduce the risk of outbreaks.
In the future
If SARS-CoV-2 can survive better in cold conditions, it’s still difficult to disentangle that contribution from the effect of people’s behaviour, says Kathleen O’Reilly, a mathematical epidemiologist at the London School of Hygiene and Tropical Medicine. “Flu has been around for hundreds of years and the specific mechanism as to why you have peaks of flu in the winter is still poorly understood,” says O’Reilly.
And even if researchers had more reliable data for SARS-CoV-2, they would see only small or negligible seasonal effects so early in the pandemic, when much of the population is still susceptible, says Relman.
Over time, however, seasonal effects could play a more important part in driving infection trends, as more people build up immunity to the virus. This could take up to five years through natural infection, or less if people are vaccinated, says Baker.
But whether a seasonal pattern emerges at all, and what it will look like, will depend on many factors that are yet to be understood, including how long immunity lasts, how long recovery takes and how likely it is that people can be reinfected, says Colin Carlson, a biologist who studies emerging diseases at Georgetown University in Washington DC.
This article is reproduced with permission and was first published on October 23 2020.