An experimental Ebola virus disease (EVD) vaccine developed in Canada is being used to try to control an outbreak in the Democratic Republic of the Congo (DRC). As of May 21, the World Health Organization (WHO) counts 57 confirmed, probable, and suspected EVD cases in the country, with 23 deaths. DRC officials reported the first cases on 8 May 2018.
The live, attenuated recombinant Ebola vaccine concept emerged from basic research about the virulence of the virus — scientists in Canada were trying to replicate American experiments that indicated that the surface glycoprotein of the virus was responsible for its virulence. They deleted the gene for the surface glycoprotein from vesicular stomatitis virus, an animal virus commonly used such experiments, and inserted the EVD glycoprotein gene. They injected mice with the engineered virus, and they did not become ill. Then, injected mice were challenged with Ebola virus, and still they remained healthy. So, they demonstrated that the glycoprotein provided protection from EVD.
The Canadian researchers published positive results of a vaccine trial in macaques in 2005 but research stalled in the absence of commercial interest in the vaccine. That changed when Ebola erupted in West Africa: by 2015 a vaccine (rVSV-ZEBOV) based on the Canadian model but licensed and produced by Merck advanced to a human clinical trial in Guinea. About 11,000 at-risk people participated in the trial, with about half receiving the vaccine. In the experimental group, no cases of EVD were reported in the 10 days after vaccine receipt, compared with 23 cases in the 6000 people who were not vaccinated.
As in the 2015 Guinea trial, health officials in DRC are giving this vaccine to people at most risk of infection: mainly healthcare workers, people responsible for burying the dead, and contacts of the ill. This strategy, known as ring vaccination, was used to control smallpox in the late stages of the Smallpox Eradication Program.
Merck has donated about 7,500 doses of the vaccine to be used in the outbreak, and Gavi, the Wellcome Trust, and UK’s Department for International Development are donating funds for the deployment of the vaccine. WHO, the DRC health ministry, and Doctors Without Borders (MSF) are coordinating vaccination activities and their followup, in addition to performing treatment and surveillance activities. The first doses were given Monday, 21 May.
Jones SM et al. Live attenuated recombinant vaccine protects nonhuman primates against Ebola and Marburg viruses. Nature Medicine. 2005 Jul;11(7):786
Smit S. Ebola vaccine put to the test in DRC. Mail & Guardian, 25 May 2018.
Young L. This “lucky mistake” from a Winnipeg lab is saving people from Ebola in the Congo. Global News, 25 May 2018.
World Health Organization. Final trials confirm Ebola vaccine provides high protection against disease. 23 December 2016.
World Health Organization. WHO supports Ebola vaccination of high risk populations in the Democratic Republic of the Congo. 21 May 2018.