After laboratory confirmation of a new Ebola case, clusters of all contacts and contacts of contacts either received immediate vaccination or delayed (21 days later) vaccination with rVSV-ZEBOV, which is a recombinant vaccine made with an attenuated livestock virus expressing a surface glycoprotein of Zaire Ebolavirus. Ebola response teams and laboratory workers were unaware of who received immediate or delayed vaccination.
Of the 2,014 people who received the vaccine immediately, none developed Ebola ten days or more after vaccination, compared with 16 confirmed cases in those in the delayed vaccination group. The effectiveness of the vaccine after different groups of patients are included is between 75% and 100%.These results come from data up to 20 July, and no new infections have since been detected in those who got the vaccine immediately. There were 43 serious adverse events reported, with one serious adverse event related to the vaccine but that resolved without further new ill effects. Assessment of serious side events is ongoing. The duration of protective effects of the vaccine is not yet known. Patients will henceforth receive immediate vaccination because that strategy has proven highly effective. The study was published in The Lancet.
The virus-based vaccine causes a temporary systemic infection, and produces a rapid immune response against the Ebola virus surface glycoprotein, conferring protection to the patient. The vaccine can induce protective immunity quickly, within a few days or a week after vaccination.
The trial used “ring vaccination”, a method that involves identifying a newly diagnosed Ebola patient, and then tracking down their contacts and contacts of contacts. An editorial to the study says that,” This procedure is not without its challenges (it was the same approach used to eradicate smallpox). To identify this often complex network of contacts required the help of family and friends in many small and dispersed communities across the most affected parts of the country. That such a trial was even possible is a testament not only to the skill of the research teams but also to the commitment of communities to defeating an epidemic that has devastated their nation.”
The study was funded by the WHO, the Wellcome Trust (UK), Médecins Sans Frontières, the Norwegian Ministry of Foreign Affairs through the Research Council of Norway, and the Canadian Government through the Public Health Agency of Canada, Canadian Institutes of Health Research, International Development Research Centre, and Department of Foreign Affairs, Trade and Development. Merck Sharp & Dohme provided the rVSV-ZEBOV vaccine.
The trial is ongoing and more data is required before wide deployment of the vaccine. But there is cause for optimism as results suggest a safe and effective Ebola vaccine is here.