BACKGROUND: Data from studies in nonhuman primates suggest that the triple 
monoclonal antibody cocktail ZMapp is a promising immune-based treatment for 
Ebola virus disease (EVD).
METHODS: Beginning in March 2015, we conducted a randomized, controlled trial of 
ZMapp plus the current standard of care as compared with the current standard of 
care alone in patients with EVD that was diagnosed in West Africa by 
polymerase-chain-reaction (PCR) assay. Eligible patients of any age were 
randomly assigned in a 1:1 ratio to receive either the current standard of care 
or the current standard of care plus three intravenous infusions of ZMapp (50 mg 
per kilogram of body weight, administered every third day). Patients were 
stratified according to baseline PCR cycle-threshold value for the virus (≤22 
vs. >22) and country of enrollment. Oral favipiravir was part of the current 
standard of care in Guinea. The primary end point was mortality at 28 days.
RESULTS: A total of 72 patients were enrolled at sites in Liberia, Sierra Leone, 
Guinea, and the United States. Of the 71 patients who could be evaluated, 21 
died, representing an overall case fatality rate of 30%. Death occurred in 13 of 
35 patients (37%) who received the current standard of care alone and in 8 of 36 
patients (22%) who received the current standard of care plus ZMapp. The 
observed posterior probability that ZMapp plus the current standard of care was 
superior to the current standard of care alone was 91.2%, falling short of the 
prespecified threshold of 97.5%. Frequentist analyses yielded similar results 
(absolute difference in mortality with ZMapp, -15 percentage points; 95% 
confidence interval, -36 to 7). Baseline viral load was strongly predictive of 
both mortality and duration of hospitalization in all age groups.
CONCLUSIONS: In this randomized, controlled trial of a putative therapeutic 
agent for EVD, although the estimated effect of ZMapp appeared to be beneficial, 
the result did not meet the prespecified statistical threshold for efficacy. 
(Funded by the National Institute of Allergy and Infectious Diseases and others; 
PREVAIL II ClinicalTrials.gov number, NCT02363322 .).