OBJECTIVE: The aim of this study was to explore any age-related change in the 
incubation period of COVID-19, specifically any difference between older (aged 
≥65 years) and younger adults.
METHODS: Based on online data released officially by 21 Chinese cities from 
January 22 to February 15, 2020, the incubation period of COVID-19 patients who 
had travelled to Hubei was studied according to age. Previous studies were 
reviewed and compared.
RESULTS: The study recruited 136 COVID-19 patients who had travelled to Hubei 
during January 5-31, 2020, stayed for 1-2 days, and returned with symptom onset 
during January 10-February 6, 2020. The median age was 50.5 years (range 1-86 
years), and 22 patients (16.2%) were aged ≥65 years. The age-stratified 
incubation period was U-shaped with higher values at extremes of age. The median 
COVID-19 incubation period was 8.3 (90% confidence interval [CI], 7.4-9.2) days 
for all patients, 7.6 (90% CI, 6.7-8.6) days for younger adults, and 11.2 (90% 
CI, 9.0-13.5) days for older adults. The 5th/25th/75th/90th percentiles were 
2.3/5.3/11.3/14.2 days for all, 2.0/5.0/10.5/13.2 days for younger adults, and 
3.1/7.8/14.4/17.0 days for older adults. There were 11 published studies on 
COVID-19 incubation periods up to March 30, 2020, reporting means of 
1.8-7.2 days, and medians of 4-7.5 days, but there was no specific study on the 
effect of age on incubation period. One study showed that severe COVID-19 cases, 
which included more elderly patients, had longer incubation periods.
CONCLUSION: Based on 136 patients with a travel history to Hubei, the epicenter 
of COVID-19, the COVID-19 incubation period was found to be longer in older 
adults. This finding has important implications for diagnosis, prevention, and 
control of COVID-19.