An interim analysis of a clinical trial of Merck & Co. and NewLink Genetics' Ebola vaccine showed that the vaccine has so far provided 100% protection from the deadly haemorrhagic virus. In the 'cluster-randomized ring vaccination trial', clinicians identified contacts of confirmed Ebola cases and randomly assigned each cluster to either immediate treatment with rVSV-ZEBOV or to delayed treatment, 21 days later. There were 0 cases of Ebola in the 4,100 people who received immediate vaccination, compared with 16 cases of Ebola in the 3,500 people who received delayed vaccination (Lancet, published online 3 Aug 2015). Further trials are ongoing to determine whether the promising interim findings hold up.

The data also provide proof of concept for the cluster-randomized ring vaccination trial design, which could be useful for the development of vaccines against other viral outbreaks.

Merck's rVSV-ZEBOV consists of a recombinant, replication-competent vesicular stomatitis virus that expresses the glycoprotein of Zaire Ebola virus. GlaxoSmithKline and Johnson & Johnson also have Ebola vaccines in clinical development.