Effectiveness and Case fatality risk among individuals vaccinated with rVSVΔG-ZEBOV-GP
Study design
Retrospective analysis
Context
The recombinant vesicular stomatitis virus–Zaire Ebola virus (rVSV-ZEBOV) vaccine is the only vaccine recommended for use to respond to Zaire ebolavirus outbreaks by SAGE. A single ring vaccination trial found the efficacy to be 100%; however, no estimates of real-world effectiveness have yet been published. Nor is there any evaluation of the protective effect of the vaccine against death among patients with confirmed Ebola virus disease.
Our role
Coordination
Partners
DRC Ministry oh Health
Effectiveness of rVSV-ZEBOV vaccination during the 10th Ebola virus disease epidemic
Methods
We conducted a retrospective test-negative case-control analysis to estimate effectiveness of rVSV-ZEBOV vaccination against Ebola virus disease (EVD) during the 2018- 2020 epidemic in the Democratic Republic of the Congo (DRC), using data on suspected cases collected at Ebola treatment centres. Missing data were imputed using multivariate imputation. Among those who reported contact with an Ebola case before symptom onset, each EVD-positive case was matched to one EVD-negative control by sex, age, health zone and month of symptom onset. Effectiveness was then estimated from the odds ratio of being vaccinated vs. unvaccinated among cases and controls, after adjusting for the matching factors.
Results
The primary study population contained 309 cases and controls each, on average, of which between 11 and 23 cases (3.6– 7.4%) and between 48 and 80 controls (16– 26%) were recorded as vaccinated at least ten days before symptom onset. We found rVSV-ZEBOV vaccination at least ten days before symptom onset was 84% effective against developing EVD (95% credible interval [70%, 92%]). There was no apparent difference in effectiveness by sex, age, or due to a change in vaccination protocol.
Conclusion
This study is the first to estimate real-world effectiveness of rVSV-ZEBOV vaccination EVD during the second largest EVD outbreak ever recorded. Our findings confirm that rVSV-ZEBOV vaccination is highly protective against developing EVD and support its reactive, targeted use in at-risk people during future outbreaks.
Read the publication
Effectiveness of rVSV-ZEBOV vaccination during the 2018–20 Ebola virus disease epidemic in the Democratic Republic of the Congo: a retrospective test-negative study.
Case fatality risk among individuals vaccinated with rVSVΔG-ZEBOV-GP
Methods
In this retrospective cohort analysis of patients with confirmed EVD admitted to Ebola health facilities in the Democratic Republic of the Congo between July 27, 2018, and April 27, 2020, we performed univariate and multivariate analyses to assess case fatality risk (CFR) and cycle threshold for nucleoprotein according to vaccination status, EVD-specific treatments, and other risk factors.
Results
We analysed all 2279 patients with confirmed EVD. Vaccination significantly lowered CFR (vaccinated: 25% (106/423) vs not vaccinated: 56% (570/1015); p<0·0001). In adjusted analyses, vaccination significantly lowered the risk of death compared with no vaccination, with protection increasing as time elapsed from vaccination to symptom onset (vaccinated ≤2 days before onset: 27% [27/99], adjusted relative risk 0·56 [95% CI 0·36–0·82, p=0·0046]; 3–9 days before onset: 20% [28/139], 0·44 [0·29–0·65, p=0·0001]; ≥10 days before onset: 18% [12/68], 0·40 [0·21–0·69; p=0·0022]; vaccination date unknown: 33% [39/117], 0·69 [0·48–0·96; p=0·0341]; and vaccination status unknown: 52% [441/841], 0·80 [0·70–0·91, p=0·0011]). Cycle threshold values were significantly higher—indicating lower viraemia— among patients who were vaccinated compared with those who were not vaccinated; the highest difference was observed among those vaccinated 21 days or longer before symptom onset (median 30·0 cycles [IQR 24·6–33·7]) compared with patients who were not vaccinated (21·4 cycles [18·4–25·9], p<0·0001).
Conclusion
To our knowledge, this is the largest observational study describing the protective effect of rVSVΔG-ZEBOV-GP vaccination against death among patients with confirmed EVD admitted to an Ebola health facility. Vaccination was protective against death for all patients, even when adjusted for EVD-specific treatment, age group, and time from symptom onset to admission.
