TThe experimental vaccine against the Ebola virus used to try to contain the epidemic in the Democratic Republic of Congo protects 97.5% of the time, according to new data released Friday by the World Health Organization.
The data – the first to be published on how the vaccine works in the epidemic – suggests a "very impressive" performance of the vaccine, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy. 39, University of Minnesota, which reviewed the report for STAT.
Of the more than 90,000 people vaccinated, only 71 developed the Ebola virus. Fifty-six of these individuals developed symptoms less than 10 days after vaccination, suggesting that the vaccine had not yet had the time to fully protect them. It is thought that it takes about 10 days for immune protection to develop after vaccination.
Only 15 people have contracted Ebola more than 10 days after vaccination, the report says. Seven of them were health workers. Nearly 29,000 health and front-line workers were among the estimated 90,000 people vaccinated between August and March 25, the reporting period.
None of the people who developed the Ebola virus 10 days or more after being vaccinated died as a result of his illness.
"In particular, there were nine deaths out of 56 cases of symptom onset 0-9 days after vaccination [who are assumed to be only partially protected by vaccination] and no deaths among people whose onset occurred 10 days or more after their vaccination [who are assumed to be protected by vaccination], Said the report.
The data was posted on the WHO website following a meeting of an expert group to assist the Director-General, Tedros Adhanom Ghebreyesus, in deciding whether to declare the outbreak in the DRC public health emergency of international concern. The committee concluded that the epidemic, although increasingly serious, is not a global threat at the moment.
The epidemic, which was first discovered last August, is the second largest ever recorded. On Thursday, there were 1,206 cases and 764 deaths. Nearly 98,000 doses of vaccine have been administered in the last eight months.
WHO has been pressured to publish vaccine efficacy data. Osterholm said that it was essential that the agency share what it finds.
"I think it's very important because it helps to give the world a better idea of how effective this vaccine is. And that the real challenges do not concern "Does the vaccine work?" Whether the vaccine is used or not, he said.
"The problem is not that your vaccine response is lower. Frankly it is exceptional. The challenge is to get it into people. "
Dr. Mike Ryan, Executive Director of the WHO Health Emergencies Program, confirmed this opinion, saying the recent outbreak of this outbreak was a result of the team's inability to respond. Fighting the outbreak of vaccinating more people in current Katwa and Butembo hot spots in these cities is too dangerous for vaccination teams to move there recently.
"We have fallen behind," Ryan said in an interview. "And we are paying the price now with increased transmission."
The vaccine, developed by Merck, is used in what is known as a ring vaccination strategy. A vaccine is offered to people who have had close and high-risk contact with known cases of Ebola. The contacts of these contacts are also offered a chance to be vaccinated. The goal is to create a wall of protection that prevents the virus from spreading.
People at high risk of exposure due to their job – health workers, ambulance drivers and people who make up the safe burial teams – are also offered a vaccine.
Although the vaccine is still not licensed, a clinical trial conducted in Guinea towards the end of the Ebola outbreak in West Africa showed that the vaccine was very effective. Based on this study, the WHO Vaccine Advisory Committee recommended that the vaccine be used as part of the arsenal of tools used to curb epidemics.
The latest data reaffirms the findings of the trial in Guinea – although the report says it's an observational study, which is a limit for this type of research.
The gold standard of testing involves randomly assigning some people to receive the vaccine and others to receive a placebo injection and to compare infection rates in both groups. But as this vaccine has been found to be effective, it would be unethical to offer placebo injections rather than the vaccine.