In 2016, Guinea, Liberia, and Sierra Leone succeeded in interrupting the longest epidemic of Ebola virus disease in global history.

Control of the epidemic was primarily achieved by implementation of effective and coordinated public health measures that involved rapid identification, isolation of cases, contact tracing, and isolation of contacts. However, the risk of re-emergence of Ebola virus disease is real, as shown by the 2017 and 2018 outbreaks in the Democratic Republic of the Congo. Consequently, along with other public health measures, efforts to develop an effective vaccine against Ebola virus disease must continue.

As of June 18, 2018, 36 completed trials, seven active and not recruiting, and seven recruiting Ebola vaccine studies are registered on ClinicalTrials.gov. The only study that has been able to provide data on clinical efficacy is the Ebola Ça Suffit vaccination trial in Guinea.

This open-label, cluster-randomised trial evaluated vaccine effectiveness in case contacts, where clusters of contacts of Ebola cases were randomised for immediate or delayed vaccination with the recombinant, replication-competent, vesicular stomatitis virus-based vaccine expressing the glycoprotein of a Zaire Ebolavirus (rVSV-ZEBOV). Although the authors estimated the vaccine efficacy to be 100% (95% CI 68·9–100, p=0·0045)

in individuals vaccinated in the immediate group compared with those eligible and randomised to the delayed group, the extent of this efficacy has been debated.

A report by the US National Academies of Sciences, Engineering, and Medicine stated that “the results suggest that the vaccine most likely provides some protection to recipients—possibly ‘substantial protection,’ as stated in the final report. However, we remain uncertain about the magnitude of its efficacy”.

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