Medical staff at the MSF-supported Ebola treatment center in Bolomba.
Epidemics

Vaccination halves mortality among people infected with Ebola

Paris, 8 February 2024 - An observational study conducted by Epicentre, Médecins Sans Frontières’ medical research and epidemiology centre, the results of which are published in The Lancet Infectious Diseases, shows for the first time that vaccination can halve mortality among people infected by Ebola.

Conducted in collaboration with the Institut National de Recherche Biomédicale (INRB) and the Ministry of Health of the Democratic Republic of Congo (DRC), this study, which analysed data collected during the 10th Ebola epidemic in the DRC, revealed that of the 2,279 confirmed Ebola patients admitted to an Ebola health facility between 27 July 2018 and 27 April 2020, the risk of dying was 56% among unvaccinated patients but fell to 25% for those who had received the vaccine. This reduction in mortality is applied to all patients, regardless of age or gender. 

Of 2,279 confirmed Ebola patients admitted to an Ebola health facility between 27 July 2018 and 27 April 2020, the risk of dying fell to 25% for those who had received the vaccine.

This new study, funded by MSF, focused on the rVSVΔG-ZEBOV-GP vaccine, the only Ebola vaccine recommended for use during an epidemic. Designed to be administered in a single dose, the rVSVΔG-ZEBOV-GP vaccine is recommended primarily for ring vaccination of people at high risk of exposure during epidemics. This strategy involves vaccinating contacts (ie, people who have had contact with an individual with confirmed Ebola virus disease), contacts of these contacts, and healthcare/frontline workers.

A phase 3 clinical trial conducted in Guinea found that the rVSVΔG-ZEBOV-GP vaccine greatly protects against Ebola virus disease Lancet. 2017 Feb 4;389(10068):505-518. doi: 10.1016/S0140-6736(16)32621-6. Epub 2016 Dec 23. Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: final results from the Guinea ring vaccination, open-label, cluster-randomised trial (Ebola Ça Suffit!) Ana Maria Henao-Restrepo et Al. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)32621-6/fulltext. Nevertheless, some people, despite being vaccinated for more than 10 days, the period considered sufficient to develop immunity, still got infected with Ebola virus disease during the 10th Ebola epidemic in the DRC. This underscores the importance of describing not only the vaccine’s effectiveness against infection, but also Its impact on mortality.

However, its impact on mortality during an epidemic had not yet been assessed, even though during the 10th Ebola epidemic in the DRC it appeared that some people got infected with Ebola despite having been vaccinated for more than 10 days, the period considered sufficient to develop immunity.

While the goal is to vaccinate people as early as possible during outbreaks, before exposure to Ebola virus disease, the results of the Epicentre study show that the vaccine protects against the risk of death from Ebola infection even when people are vaccinated "late", ie, after having been exposed to Ebola virus disease. In addition, no antagonistic effect between vaccination and treatment against Ebola was observed in this study.

“Vaccination after exposure to a person infected with Ebola virus disease, even when administered shortly before the onset of symptoms, still confers significant protection against death," explains Rebecca Coulborn, epidemiologist at Epicentre. “The reduced risk of death due to vaccination is in addition to the reduction due to Ebola-specific treatment, regardless of the delay before treatment.”

This study provides further evidence of the importance of vaccination against Ebola during the epidemics that regularly occur in sub-Saharan Africa. These are most often caused by the Zaire ebolavirus species, which is associated with high mortality. Since 2019, two vaccines, rVSVΔG-ZEBOV-GP and Ad26.ZEBOV/MVA-BN-Filo, have obtained WHO prequalification against this strain.

“In addition to the direct benefit, our results allow us to consider combining vaccination and treatment of patients who have been in direct contact with a person with confirmed Ebola virus disease to reduce the risk of illness and death”, says Etienne Gignoux, Director of Epicentre's Epidemiology and Training Department.

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Press Release 8 February 2024