Ebola vaccine clinical trial results suggest vaccine is safe and highly efficacious

Interim results from the phase 3 clinical trial of the rVSV-ZEBOV vaccine show that the vaccine “might be highly efficacious and safe” in preventing Ebola, according to researchers who conducted the trial. The randomised trial involved 7651 individuals who were either vaccinated immediately or provided delayed vaccination 21 days after the start of the trial. No cases of Ebola were reported in the immediate vaccination group while 16 individuals were infected in the delayed vaccination group 10 days after being administered rVSV-ZEBOV. The results of the study are published in The Lancet.


Dr. Jesse L. Goodman, Professor of Medicine, Georgetown University Medical Center (webpage): 

Expertise: infectious diseases and public health.  Dr. Goodman formerly served as the U.S. Food and Drug Administration Chief Scientist and Deputy Commissioner 

“The paper provides exciting preliminary evidence that a candidate Ebola vaccine, VSV-EBOV, is likely to be effective in preventing secondary Ebola infections when given quickly to contacts of cases in disease clusters, as well as the contacts of those contacts.

“No Ebola cases were reported 10 or more days after vaccination among the 2048 consenting subjects in the immediate vaccination clusters vs. 11 cases among the 1930  in clusters where vaccination was delayed for 21 days.

“While this preliminary analysis is exciting, and the results are very encouraging, there are some issues about the study that raise potential uncertainties. These include that participants and investigators knew if subjects were getting vaccine early or late, which may have affected their behavior, that a large number of eligible individuals in both groups did not get vaccinated, and that Ebola cases were apparently identified through normal disease surveillance mechanisms, which might miss some cases, particularly if less severe. In addition, it appears that some aspects of study design, such as excluding cases occurring within the 10 day interval after vaccination, were implemented only after the study began.”

“The complete study data (and the study is still in progress) must be reviewed, including by appropriate regulatory authorities. Nonetheless, the degree of protection reported seems convincing.”

“While more information is needed, this is very good news today and suggests that the rVSV-EBOV Ebola vaccine is effective and can be an important tool in outbreak control, including through ring vaccination, which can be continued to help control this outbreak.  We should be grateful to the study participants and to those who carried out and supported the study under challenging circumstances. Depending on what more is learned from this and other studies, Ebola vaccines are likely to be important tools to help in controlling and even preventing future epidemics and in protecting others at risk, such as health workers.”


Declared interests (see GENeS register of interests policy):

No interests declared



Efficacy and effectiveness of an rVSV-vectored vaccine expressing Ebola surface glycoprotein: interim results from the Guinea ring vaccination cluster-randomised trial’ by Ana Maria Henao-Restrepo et al. published in the Lancet on Friday 31 July 2015

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