Abstract
BACKGROUND
The rVSV-ZEBOV vaccine is the only WHO prequalified Ebola vaccine recommended for use to respond to Zaire ebolavirus outbreaks by the Strategic Advisory Group of Experts (SAGE). A single ring vaccination trial found the efficacy to be 100%, and despite widespread use during several outbreaks, no effectiveness estimates are currently available in the literature.
METHODS
We conducted a retrospective test-negative case-control analysis to estimate effectiveness of rVSV-ZEBOV vaccination against EVD during the 2018 - 2020 epidemic in the DRC, using a database of over 60,000 suspected cases from all Ebola treatment centres. Each EVD-positive case was matched to one EVD-negative control by sex, age, health zone and month of symptom onset, and effectiveness estimated from the odds ratio of being vaccinated vs. unvaccinated among cases and controls, after adjusting for the matching factors. Missing demographic data and vaccination-onset delays were imputed using multivariate imputation.
FINDINGS
Among all 26,438 eligible individuals, 4.8% were EVD-positive. 3.1% of cases and 5.1% of controls reported to be vaccinated at least ten days before symptoms onset. Effectiveness of rVSV-ZEBOV vaccination when vaccinated at least ten days before symptom onset was 84% (95% credible interval [70%, 92%]). There was no evidence of a change in effectiveness by age, sex, nor due to change in dosing. Estimates were robust to methodological assumptions.
INTERPRETATION
This analysis is the first study to provide estimates of real-world effectiveness of the rVSV-ZEBOV vaccine against EVD, amid the, to date, most widespread use of the vaccine during the second largest EVD outbreak ever recorded. Our findings confirm that rVSV-ZEBOV vaccination is highly protective against EVD and support its use to control EVD outbreaks, even in challenging contexts such as the eastern DRC.
