A single dose of an experimental vaccine was up to 100% effective at preventing Ebola infection among those who had come into contact with recently infected individuals, according to interim results of an open-label trial conducted earlier this year in Guinea.
The study, which took place during an Ebola outbreak, included 90 clusters totaling 7,651 people who either had direct contact with someone recently diagnosed with Ebola or had contact with a direct contact. Children and pregnant or breastfeeding women were not eligible for the vaccine, and some study participants refused vaccination.
Consenting and eligible participants in 48 clusters were randomized to receive the vaccine (rVSV-ZEBOV) immediately after randomization; those in the remaining 42 clusters were vaccinated 21 days after randomization. Given that the incubation period of the virus is 10 days, the primary outcome was laboratory-confirmed Ebola infection at least 10 days after randomization to either immediate or delayed vaccination.
None of the 2,014 immediately vaccinated individuals contracted Ebola during that time, while 16 of the 1,0121 adults in the delayed vaccination group became infected, showing vaccine efficacy of 100%, Dr. Ana Maria Henao-Restrepo of the World Health Organization, Geneva, and her colleagues wrote in the Lancet.
At the cluster level, vaccine efficacy was 76% when all individuals – including children and pregnant and lactating women who were not vaccinated – were included. A total of 43 serious adverse events were reported, one of which was deemed directly related to vaccination.
“The interim results of [this trial] suggest that the efficacy of a single injection of rVSV-ZEBOV to prevent Ebola virus disease might be high, that protection can be established quickly, and that the vaccine might be effective at the population level when delivered by ring vaccination ...” the investigators wrote. The trial will be continued.
The results of this research project “will be the subject of intense scientific scrutiny and debate,” but a team under the World Health Organization’s leadership and the GAVI Alliance are ready to respectively support, and fund procurement and deployment of the vaccine, if it gets licensed, according to an editorial.
Read the full study in The Lancet (http://www.thelancet.com/pb/assets/raw/Lancet/pdfs/S0140673615611175.pdf ).