New Ebola Vaccine Delivered 100% Protection

The rVSV-ZEBOV vaccine produced no Ebola cases 10 days after vaccination


An experimental Ebola vaccine was highly protective against the deadly virus in a major phase III clinical trial. This vaccine is the first to prevent infection from one of the most lethal known pathogens.

The vaccine, called rVSV-ZEBOV, was studied in Guinea, during 2015.

Among the 5,837 people who received the rVSV-ZEBOV vaccine, no Ebola cases were recorded 10 days or more after vaccination.

The trial was led by the World Health Organization (WHO), together with Guinea’s Ministry of Health and other international partners.

“These compelling results show that when the next Ebola outbreak hits, we will not be defenceless,” said Dr Marie-Paule Kieny, WHO’s Assistant Director-General for Health Systems and Innovation, and the study’s lead author.

Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a severe, often fatal illness in humans. The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission. The average EVD case fatality rate is around 50%.

The virus family Filoviridae includes three genera: Cuevavirus, Marburgvirus, and Ebolavirus. There are five species that have been identified: Zaire, Bundibugyo, Sudan, Reston and Taï Forest.

Ebola is introduced into the human population through close contact with the blood, secretions, organs or other bodily fluids of infected animals such as chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest.

The vaccine’s manufacturer, Merck, Sharpe & Dohme, this year received Breakthrough Therapy Designation from the United States Food and Drug Administration (FDA) and PRIME status from the European Medicines Agency, enabling faster regulatory review of the vaccine once it is submitted.

Since Ebola virus was first identified in 1976, sporadic outbreaks have been reported in Africa. But the 2013-2016 West African Ebola outbreak, which resulted in more than 11,300 deaths, highlighted the need for a vaccine.

In addition to showing high efficacy among those vaccinated, the trial also shows that unvaccinated people were indirectly protected from Ebola virus through the vaccination approach (so-called “herd immunity”).

However, the authors note that the trial was not designed to measure this effect, so more research will be needed. It was not possible to collect biological samples from people who received the vaccine in order to analyse their immune response.

Additional studies are ongoing to provide more data on the safety of the vaccine in children and other vulnerable populations such as people with HIV.

The rapid development of rVSV-EBOV contributed to the development of WHO’s R&D Blueprint, a global strategy to fast-track the development of effective tests, vaccines and medicines during epidemics.

The rVSV-ZEBOV trial is funded by WHO, with support from the Wellcome Trust, the United Kingdom Department for International Development, the Norwegian Ministry of Foreign Affairs to the Norwegian Institute of Public Health through the Research Council of Norway, the Canadian Government through the Public Health Agency of Canada, Canadian Institutes of Health Research, International Development Research Centre and Department of Foreign Affairs, Trade and Development and Médecins Sans Frontières.

The trial team includes experts from The University of Bern, the University of Florida, the London School of Hygiene and Tropical Medicine, Public Health England, the European Mobile Laboratories among others. The trial was designed by a group of experts including the late Professor Donald A. Henderson of John Hopkins University, who led the WHO smallpox eradication effort by using the ring vaccination strategy.

No conflicts of interest were disclosed. Pricing for the rVSV-ZEBOV vaccine was not presented.