Published in the Lancet Infectious Disease, a study has revealed that 10 days after vaccination, the risk of developing Ebola is reduced by 84 per cent in vaccinated people compared to non-vaccinated people. The study analysed data collected during the largest epidemic recorded in the DRC, during which 3,470 cases and 2,287 deaths were registered between 2018 and 2020. It was conducted by Epicentre, the epidemiology and medical research arm of Médecins Sans Frontières (MSF), in collaboration with the Institut National de Recherche Biomédicale (INRB) and the Ministry of Public Health of the Democratic Republic of Congo (DRC).
The study, funded by MSF, focused on the rVSVΔG-ZEBOV-GP vaccine, the only Ebola vaccine recommended for use by the World Health Organization for people at high risk of contracting the disease during an epidemic. “This study dispels uncertainties about the vaccine’s actual effectiveness: it is the first published study to evaluate the effectiveness of the rVSVΔG-ZEBOV-GP vaccine outside of a clinical trial. It was carried out during the second largest Ebola epidemic on record,” says Sophie Meakin, epidemiologist with Epicentre.
Designed to be administered as a single dose, the vaccine was used as part of a ring strategy – vaccinating contacts (i.e. people who have been in contact with a person in whom Ebola infection has been confirmed), contacts of these contacts and healthcare staff. During the 2018-2020 Ebola epidemic in the DRC, vaccination began in August 2018 and over 300,000 people were vaccinated.
Based on a test negative study, the study showed vaccination with rVSV-ZEBOV offered high protection against the development of Ebola virus disease from the tenth day after vaccination. Vaccine Effectiveness was estimated by comparing Ebola PCR test positivity rates between vaccinated and non-vaccinated people. All of them had reported contact with an Ebola-infected person, and had been tested by PCR at healthcare facilities to confirm whether or not they were carriers of the disease. In all, 309 people tested PCR-positive and 309 showed symptoms of suspected Ebola but tested negative. Vaccination reduced the risk of developing the disease by 84 per cent after 10 days. Slight variations were observed according to gender: the vaccine was 80 per cent effective in women, 86 per cent in men.
Steve Ahuka, head of virology at INRB and medical professor at the University of Kinshasa, emphasises the importance of systematic and rigorous data collection during epidemics, despite the challenges: “These are unique opportunities to deepen our knowledge of often rare diseases, and thus improve the management of future epidemics, develop new control tools and determine the best strategies for using them effectively”.
Recently, Epicentre also demonstrated through further study and clinical trial that vaccination halved mortality among people infected with Ebola. These studies reinforce the importance of rapidly vaccinating people potentially exposed to the Ebola virus as soon as epidemics begin.
