Ebola vaccine halves mortality rate, new data show
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Patients with confirmed Ebola virus disease were around half as likely to die if they were vaccinated against the virus than if they were not, results from a study showed.
The observational study included more than 2,200 patients admitted to an Ebola treatment facility over nearly 2 years in the Democratic Republic of the Congo (DRC), where the vaccine has been deployed to stop multiple outbreaks.
The vaccine was originally tested nearly a decade ago during the West African Ebola epidemic, where initial trial results indicated it could be 100% effective at preventing Ebola. A subsequent trial conducted by the DRC’s National Institute for Biomedical Research and WHO during a large outbreak in the DRC determined the vaccine was 97.5% effective.
The new study was the first time that researchers calculated Ebola mortality among people who had received the vaccine and then experienced a breakthrough infection. The results were published in The Lancet Infectious Diseases.
Researchers analyzed outcomes from 2,279 patients with confirmed Ebola virus disease who were treated in the DRC between July 27, 2018, and April 27, 2020, a study period that coincided with the second largest Ebola outbreak ever recorded, which killed more than 2,200 people.
According to their analysis, the fatality rate among 423 participants who had received the vaccine was approximately 25%. Among unvaccinated participants, it was 56%.
The vaccine’s protective effect increased the longer a person had been vaccinated, with the mortality rate falling from 27% among participants vaccinated just 2 days or fewer from the onset of their symptoms to 18% among those who received the vaccine 10 days or more before they got sick. Most vaccinated participants were aged 15 to 59 years.
The results demonstrate that “vaccine failure is still compatible with high effectiveness,” the researchers wrote.
They listed several potential reasons other than primary vaccine failure for the more than 400 breakthrough infections identified during the study, including cold chain failure, inadequate dosing or injection technique, and immunosuppression.
“Our results reinforce the importance of vaccinating populations who are at risk of exposure to Ebola virus to reduce the risk of infection and — if infection occurs — the risk of death,” the researchers wrote.
References:
- Coulborn RM, et al. Lancet Infect Dis. 2024;doi:10.1016/S1473-3099(23)00819-8.
- Henao-Restrepo AM, et al. Lancet. 2016;doi:10.1016/S0140-6736(16)32621-6.
- WHO. Preliminary results on the efficacy of rVSV-ZEBOV-GP Ebola vaccine using the ring vaccination strategy in the control of an Ebola outbreak in the Democratic Republic of the Congo: an example of integration of research into epidemic response. https://www.who.int/publications/m/item/preliminary-results-on-the-efficacy-of-rvsv-zebov-gp-ebola-vaccine-using-the-strategy-in-the-control-of-an-ebola-outbreak. Published April 10, 2019. Accessed Feb. 12, 2024.
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