NEW YORK — An experimental Ebola vaccine being tested in the West African nation of Guinea during the outbreak of the disease has shown promising initial results, according to a report on the clinical trial.
The report, published Friday in the British medical journal The Lancet, said the vaccine was found to be 100 percent effective in people treated immediately after coming in contact with the viral disease, although more research is needed to determine how long the results will last.
The report analyzed 7,651 individuals, more than 3,500 of whom were vaccinated, and indicated that the vaccine “might be highly efficacious and safe.”
Dr. Margaret Chan, director general of the World Health Organization, said if the preliminary results are confirmed, the vaccine ‘‘is going to be a game-changer.’’
‘‘It will change the management of the current Ebola outbreak and future outbreaks,’’ Chan said, while noting that it was not a silver bullet to head off future outbreaks. “There is no replacement for very strong and good, resilient health systems with the capability for surveillance.”
The clinical trial involved inoculating people who had come into contact with Ebola patients, and the contacts of those contacts. Some clusters of people were vaccinated immediately, while others, assigned randomly, were vaccinated after 21 days, the incubation period of the virus.
Those groups were compared beginning 10 days after they entered the study, to give the vaccine time to set off an immune response, and because some of the contacts might already have been incubating the virus.
After 10 days, none of those in the immediate vaccination group subsequently contracted Ebola, whereas 16 of the people eligible for the study who were not immediately vaccinated came down with the disease.
Those results were highly significant, the authors reported, indicating the vaccine was between 75 and 100 percent efficacious for all those vaccinated. And the researchers observed that there were no Ebola cases in vaccinated patients after the first six days. The authors of the study also found few side effects in the adults who were vaccinated.
The study was led by WHO, the Guinean Health Ministry, Doctors Without Borders, the nonprofit Epicentre research center, and the Norwegian Institute of Public Health, among many other contributing organizations.
Researchers working at the Public Health Agency of Canada created the experimental vaccine, which combines a piece of the virus’s covering with an animal virus to set off an immune response against Ebola. It was licensed by NewLink Genetics, a biopharmaceutical company based in Ames, Iowa, in 2010, and then in November by Merck Vaccines, a unit of New Jersey-based Merck & Co.
The next step will be submitting the data from this study and several others, including safety results, to regulatory bodies such as the US Food and Drug Administration. Then the vaccine can be considered for licensure.
“We’re fully committed to working with regulatory authorities to define what the requisite data is and provide it as quickly as we can do so,” said Dr. Mark Feinberg, chief public health and scientific officer at Merck Vaccines.
“In the past, I think there wasn’t a strong belief that we needed an Ebola vaccine or that it would actually be possible to develop an Ebola vaccine,” Feinberg said. “Now I think there’s unanimity.”
Because no placebos were used, volunteers knew whether they had received the vaccine, which could have influenced the study’s outcome. Choices like this, some of which were highly contentious on ethical and scientific grounds, were made to be pragmatic in the context of an emergency, said Jeremy Farrar, director of the Wellcome Trust, a major supporter of the research.
The fact that promising results were obtained despite certain compromises in scientific rigor, he said, “in a sense vindicates the design and approach that was taken and moves the field forward.”
This was the first time in memory that a vaccine’s effectiveness has been studied with a so-called ring vaccination approach, inoculating all of those around the occurrence of an infectious disease, according to one of the study’s senior authors, Dr. John-Arne Rottingen of the Norwegian Institute of Public Health. That vaccination strategy was used to help eradicate smallpox.
“I thought the only way to be successful would be to follow the epidemic and try to vaccinate in high-risk individuals,” Rottingen said. This approach ended up producing results even when the country only had a small number of cases, distributed across a large area.
Other studies in Liberia and Sierra Leone, where the virus also raged, are continuing, but they are not expected to produce results on the effectiveness of the vaccine given the low numbers of patients in recent weeks, and the design, which did not target contacts of Ebola patients.
The WHO reported seven confirmed cases last week in the region, the lowest number of new Ebola patients in well over a year. On Friday, the United Nations secretary-general was expected to announce the end of a special mission for Ebola emergency response.
Vaccinations began in late March in Guinea. The plan was to vaccinate 10,000 people in 190 rings. But because of the positive interim results, a safety monitoring board recommended that the study be published and that the design be altered to provide immediate vaccination to all eligible volunteers.