Abstract
A recently published Ebola vaccine trial claimed an almost perfect result with no cases of Ebola after the vaccine had time to take effect - a vaccine efficacy of 100%. This article is a detailed review of the information published about the trial and, particularly, this claim. The trial design was sub-optimal because randomization was only partial (and one treatment arm was unrandomized), it was unblinded and did not use a placebo. Less information on the comparison arm that substituted for a placebo was provided, such as adverse events, compared to the active treatment arms. There was little baseline information on the trial participants, which is particularly important to ensure equivalence of the arms of a trial that was not fully randomized. In particular, Ebola tests were not performed at baseline, so the possibility of false positive test results or pre-existing asymptomatic cases exists. Ebola symptoms and adverse reactions following vaccination seen during the trial were very similar, allowing diagnostic bias. The exclusion of Ebola cases among the vaccinated during the 10 days after randomization is an arbitrary decision for an infection with an incubation period of 2 to 21 days and not a substitute for comparing vaccine to placebo. Considering the entire 31-day reporting period, two subgroups of unvaccinated participants had significantly fewer cases of Ebola than the two vaccinated groups. The problems with this trial are so grave that it cannot be taken as even weak evidence that the vaccine trialed is effective at preventing Ebola Virus Disease (EVD).
Highlights
A paper published in 2016 announced highly positive results for an Ebola virus vaccine, with no infections in people vaccinated, after the vaccine had time to take effect (Henao-Restrepo et al, 2016)
If safe and effective it could reduce the scourge of Ebola epidemics, but if not it could add the cost of adverse reactions to the vaccine to an unchanged burden of Ebola outbreaks and discourage other responses to Ebola prevention
Bleeding has even been removed from its name, which is Ebola Virus Disease (EVD)
Summary
A paper published in 2016 announced highly positive results for an Ebola virus vaccine, with no infections in people vaccinated, after the vaccine had time to take effect (Henao-Restrepo et al, 2016). This resulted in four cases in the Delayed group, that occurred in the days following vaccination on day 21, being relegated to a footnote in the supplementary materials Another exclusion period is the time after the end of the observation period during which, “vaccinated cases of Ebola virus disease with an onset of more than 31 days after random assignment were censored” (Henao-Restrepo et al, 2016, Outcomes). This shows that there is no evidence that the vaccine protects anyone for more than 21 days and leaves open the possibility that cases of Ebola in vaccinated participants were detected, but not published.
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