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August 3, 2015
The experimental Ebola vaccine rVSV-ZEBOV may offer highly effective and rapid protection against the virus with a single injection, according to the first interim results reported from the Ebola ça Suffit cluster randomized phase 3 trial conducted in Guinea (Henao-Restrepo AM et al. Lancet. doi:10.1016/S0140-6736(15)61117-5 [published online August 3, 2015]).
The trial, sponsored and led by the World Health Organization, used a ring vaccination strategy that did not include a placebo control group. According to the researchers, such a cluster or ring vaccination approach can be effective in resource-poor countries where the incidence of Ebola is low in the general population.
When a new Ebola case was diagnosed, researchers traced all individuals who may have had contact with a sick individual and contacts of contacts. Adults in that cluster were randomly assigned to receive either immediate vaccination or delayed vaccination 21 days after randomization. Participants were visited at home on days 3, 14, 21, 42, 63, and 84 after vaccination to record any adverse events.
Ninety clusters received either immediate vaccination (4123 adults) or delayed vaccination (3528 adults); no cases of Ebola virus disease (EVD) were recorded 10 days after randomization in those clusters who received the vaccine immediately, compared with 16 cases in clusters who received delayed vaccination. The estimated efficacy of rVSV-ZEBOV was 100%. Of the 43 serious adverse events, 1 was causally related to the vaccine.
For all members of the clusters, including nonvaccinated children and pregnant women, the estimated reduction in the risk of EVD was approximately 76%.
According to an editorial accompanying the study, more data on vaccine efficacy are needed before wide deployment.