Four years since the onset of the 2013–2016 Ebola outbreak, researchers have solid clinical evidence that a vaccine can reduce the spread of the deadly haemorrhagic fever.

Researchers set up an open-label phase III trial designed to test the vaccine in people who may have already come into contact with Ebola. Around 2,100 subjects were vaccinated immediately with Merck & Co.'s rVSV-ZEBOV, and a similar number of subjects in a control arm received a delayed vaccination 21 days later. No Ebola cases occurred within 10 days or more of treatment in the patients who received immediate vaccination, whereas 23 cases occurred in the control group, the researchers reported in The Lancet .

rVSV-ZEBOV consists of a recombinant vesicular stomatitis virus that expresses the Zaire Ebolavirus glycoprotein. Johnson & Johnson and GlaxoSmithKline are also running late- and mid-stage trials of Ebola vaccines.