by Ruggiero Corcella
The results of an observational study by Doctors Without Borders have been published in The Lancet Infectious Diseases. Interview with epidemiologist Rebecca Coulborn of MSF: «No new epidemic, but even just one case is enough to declare it»
Ten years after the worst Ebola epidemic in history, which hit three West African countries causing more than 11,300 deaths, an observational study conducted by Epicentre, the medical and epidemiological research center of Doctors Without Borders (MSF), shows that the Vaccination against Ebola can halve the mortality rate. The results of the study published in The Lancet Infectious Diseases highlight that mortality among unvaccinated patients was 56% compared to 25% of those who had received the vaccine.
The situation today
What is the situation on the epidemiological front today? «As far as we know, there is no ongoing Ebola epidemic – replies Rebecca Coulborn, epidemiologist at the MSF Epicentre center –. The most recent was in Uganda, which was declared closed on January 11, 2023. For your information, it only takes one case to declare an epidemic. Historically, we had little more than palliative care to offer patients. We now have new therapies and vaccines against the deadliest strain of Ebola. These are important steps for public health preparedness and response. These tools can dramatically improve the health of Ebola-affected populations, both by preventing the disease entirely and, if infected, decreasing the risk of severe Ebola disease, including death. It is important that all countries at risk of Ebola have access to these life-saving tools.”
How the vaccine works
This study, carried out in collaboration with the National Institute of Biomedical Research (INRB) and the Ministry of Health of the Democratic Republic of Congo (DRC), analyzes data collected during the tenth Ebola epidemic in DRC on 2,279 confirmed hospitalized Ebola cases in a healthcare facility between 27 July 2018 and 27 April 2020 and refers to all patients, regardless of gender and age. The study, funded by MSF, focuses on the rVSVΔG-ZEBOV-GP vaccine, the only Ebola vaccine recommended during epidemics by the World Health Organization. (WHO).
«Being pre-qualified by the WHO means that a vaccine has met specific global standards of quality, safety and efficacy/performance. – explains Rebecca Coulborn -. WHO pre-qualification is a regulatory process that is usually followed by individual countries authorizing/registering a new vaccine in their countries rVSVΔG-ZEBOV-GP (Ervebo, Merck & Co, Rahway, NJ, USA) was pre-qualified -qualified by WHO in November 2019. Johnson & Johnson’s Ebola vaccine, Zabdeno (Ad26.ZEBOV) and Mvabea (MVABN-Filo), was pre-qualified by WHO in April 2021.”
«Ring» vaccination
Developed to be administered as a single dose, the rVSVΔG-ZEBOV-GP vaccine is primarily recommended for ring vaccination of people at high risk of exposure during epidemics. This strategy involves vaccinating contacts (people who have had contact with an individual infected with the Ebola virus), contacts of contacts, healthcare workers and frontline workers.
A phase 3 clinical trial conducted in Guinea demonstrated that the rVSVΔG-ZEBOV-GP vaccine significantly protects against Ebola1 virus infection. However, some people, despite having been vaccinated for more than 10 days, a period considered sufficient to develop immunity, were still infected with the Ebola virus during the tenth epidemic in the DRC. This highlights the importance of evaluating not only the vaccine‘s effectiveness against infection, but also its impact on mortality.
The vaccine also works if administered after infection
However, the impact of the vaccine on mortality during an epidemic had not yet been assessed, although during the tenth Ebola epidemic in DRC it emerged that some people became infected with Ebola despite having been vaccinated for more than 10 days, the period considered enough to develop immunity. Although the goal remains to vaccinate people as early as possible during epidemics, i.e. before exposure to the Ebola virus, the results of the MSF Epicentre study show that the vaccine significantly reduces mortality even when administered “late” , that is, after exposure to the virus. Furthermore, the study found no antagonistic effect between vaccination and Ebola treatment.
“Vaccination after contact with a person affected by the Ebola virus, even if administered shortly before the onset of symptoms, still confers significant protection against death” says Rebecca Coulborn. “The reduced risk of death thanks to vaccination adds to the risk reduction given by specific treatment against Ebola, regardless of the delay before treatment.” This study provides further evidence of the importance of Ebola vaccination during epidemics, which occur regularly in Sub-Saharan Africa. These are often caused by the Ebola Zaire virus, which causes high mortality. “The next step – adds the epidemiologist – would be to evaluate vaccination and preventive treatment for people who we know have had high-risk exposure, which means they have a very high probability of developing the disease”.
Since 2019, two vaccines have obtained prequalification from the WHO against this strain: rVSVΔG-ZEBOV-GP and Ad26.ZEBOV/MVA-BN-Filo. “In addition to the direct benefits, our results allow us to consider a possible combination of vaccination with the treatment of patients who have been directly in contact with confirmed cases of Ebola to reduce the risk of disease and death,” says Etienne Gignoux, director of the Epidemiology and training department of Epicentre.
What is the Ebola virus
Ebola was discovered in 1976 in the Democratic Republic of Congo (DRC). There are several variants of the disease, with the Zaire species being the most common over the last decade. The most recent epidemics have affected in particular the Democratic Republic of Congo (the twelfth epidemic in 2021) and Uganda (2019 and 2022). During the Ebola epidemic in West Africa (Liberia, Guinea and Sierra Leone) in 2014, 28,646 people were infected.
Around a third of all patients were admitted to an MSF health centre, where 2,478 people were saved. MSF has been on the front line since the first days of the epidemic and at the peak of the spread it employed up to 4,000 national and 325 international workers, of which over 70 were Italian. Later, it launched projects dedicated to survivors and today continues to provide services to support healthcare systems devastated by the epidemic
Treatments and new vaccines under study
How many people have been vaccinated so far? Are there new campaigns planned? «As for the number of people vaccinated, we don’t have the answer. There are many other Ebola vaccines being studied, including those that aim to protect against other strains of the Ebola virus and other viral hemorrhagic fevers.” «Continued research is essential to protect populations at risk. As for non-vaccine resources, we also have two treatments that have proven to be the most effective against Ebola virus disease: mAb114 (e.g., ansuvimab-zyk; Ebanga, Ridgeback Biotherapeutics, Miami, FL, United States of America) and REGN-EB3 (i.e., atoltivimab, maftivimab, and odesivimab; Inmazeb, Regeneron Pharmaceuticals, Tarrytown, NY, United States of America)’.
“In terms of other things we can offer, there is also supportive care provided to patients (for example, treatments that are not specific to Ebola, such as malaria treatment for those who are also infected with malaria). And there is also increasing use of decentralized models of care (for example, bringing testing and treatment closer to where the population lives, rather than having Ebola health facilities further away from the population, centralized in larger cities). large)”, concludes the epidemiologist.
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February 17, 2024 (modified February 17, 2024 | 2.49 pm)
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