Team members of the WHO Ebola vaccine trial, at work in Katongourou, Guinea.
Photo: WHO/S.Hawkey

WHO confirms effectiveness of Ebola vaccine

The so far only large-scale study of an Ebola vaccine tested on human beings has now demonstrated reliable protection against the dangerous virus while displaying good tolerability.

An experimental Ebola vaccine was highly protective against the deadly virus in a major trial in Guinea, according to results published in The Lancet in late December. The vaccine is the first to prevent infection from one of the most lethal known pathogens, and the findings add weight to early trial results published in 2015.

The vaccine, called rVSV-ZEBOV, was studied in a trial involving 11,841 people in Guinea during 2015. Among the 5,837 people who received the vaccine, no Ebola cases were recorded ten days or more after vaccination. In comparison, there were 23 cases ten days or more after vaccination among those who did not receive the vaccine.

"While these compelling results come too late for those who lost their lives during West Africa's Ebola epidemic, they show that when the next Ebola outbreak hits, we will not be defenceless," said the study’s lead author Dr Marie-Paule Kieny, Assistant Director-General for Health Systems and Innovation at the World Health Organization (WHO). The trial was led by WHO together with Guinea’s Ministry of Health, Medecins sans Frontières and the Norwegian Institute of Public Health, in collaboration with other international partners.

Since the 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. The trial took place in the coastal region of Basse-Guinée, the area of Guinea still experiencing new Ebola cases when the trial started in 2015. The trial used an innovative design, a so-called “ring vaccination” approach – the same method used to eradicate smallpox.

When a new Ebola case was diagnosed, the research team traced all people who may have been in contact with that case within the previous three weeks, such as people who lived in the same household, were visited by the patients, or were in close contact with them, their clothes or their linen, as well as certain “contacts of contacts”. A total of 117 clusters (or "rings") were identified, each made up of an average of 80 people.

Initially, rings were randomised to receive the vaccine either immediately or after a three-week delay, and it was only offered to adults over 18 years. After interim results were published showing the vaccine’s efficacy, it was immediately offered to all rings, and the trial was also opened to children older than six years.
In addition to showing high efficacy among those vaccinated, the trial shows that unvaccinated people in the rings were indirectly protected from Ebola virus through the ring 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.

To assess safety, people who received the vaccine were observed for 30 minutes after vaccination, and at repeated home visits up to twelve weeks later. Approximately half of them reported mild symptoms soon after vaccination, including headache, fatigue and muscle pain, but recovered within days without long-term effects. Two serious adverse events were judged to be related to vaccination (a febrile reaction and one anaphylaxis), and one was judged to be possibly related (influenza-like illness). All three recovered without any long-term effects.

The drug could be on the market by 2018. The rights to it are held by the US Merck corporation. Further vaccines by other manufacturers are currently being tested.

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Publication               Download article             Rural 21 issue on Ebola

(WHO/sri)