Results from an interim analysis of a phase 3 trial of an investigational Ebola vaccine demonstrated 100% efficacy in more than 4,000 adults in Guinea.
“This is an extremely promising development,” WHO Director-General Margaret Chan, MD, said in a press release. “The credit goes to the Guinean government, the people living in the communities and our partners in this project. An effective vaccine will be another very important tool for both current and future Ebola outbreaks.”
rVSV-ZOBOV is a recombinant, vesicular stomatitis virus-based vaccine developed by the Public Health Agency of Canada and licensed to NewLink Genetics and Merck. Its development was supported by the United States and Canadian governments, among others. Testing of the vaccine began on March 23.
In a phase 3, open-label, randomized trial, clusters of all contacts — as well their contacts — of confirmed Ebola cases were randomly assigned in a 1:1 ratio to immediate or delayed vaccination (21 days later). The interim analysis included 48 clusters, with 4,123 contacts of nearly 100 Ebola patients.
“The ‘ring’ vaccination method adopted for the vaccine trial is based on the smallpox eradication strategy,” John-Arne Rttingen, MD, PhD, director of the division of infectious disease control at the Norwegian Institute of Public Health and chair of the study steering group, said in the release. “The premise is that by vaccinating all people who have come into contact with an infected person, you create a protective ‘ring’ and stop the virus from spreading further. This strategy helped us to follow the dispersed epidemic in Guinea, and will provide a way to continue this as a public health intervention in trial mode.”
At least 10 days after randomization, there were no new cases detected among those who were immediately vaccinated, compared with 16 confirmed cases in individuals who delayed vaccination, according to the researchers. The estimated vaccine efficacy was 100% (95% CI, 74.7-100).
On July 26, the trial stopped randomization to allow people at risk for Ebola virus disease to receive the vaccine immediately, and to collect more data needed for the vaccine’s eventual licensure, according to WHO. Guinean health authorities and an ethics review committee have approved a continuation of the trial, which will now include participants aged 13 to 17 years and possibly those aged 6 to 12 years.
“In parallel with the ring vaccination, we are also conducting a trial of the same vaccine on front-line workers,” Bertrand Draguez, MD, medical director of Médecins Sans Frontières, said in the release. “These people have worked tirelessly and put their lives at risk every day to take care of sick people. If the vaccine is effective, then we are already protecting them from the virus.
“With such high efficacy, all affected countries should immediately start and multiply ring vaccinations to break chains of transmission and vaccinate all front-line workers to protect them.” – by John Schoen
Disclosure: The vaccine candidate is licensed to NewLink Genetics Corp. and Merck. Henao-Restrepo reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.