A vaccine for The Ebola strain at the origin of the epidemic in the Democratic Republic of Congo and Uganda, it will likely take months to conduct human trials, and there is no guarantee it will work, the World Health Organization said Wednesday.
There is currently no approved vaccine for the Bundibugyo strain of the Ebola virus.
There are two potential vaccine candidates, but neither is ready to move to human testing, Dr. Vasee Moorthy, head of WHO’s research and development plan, told a news conference.
The more promising of the two could take six to nine months before enough doses are ready for testing, Moorthy said. The other could be available in two to three months, but has not yet shown convincing results in animal studies.
“It will depend on animal data whether this is considered a promising vaccine candidate against Bundibugyo,” he said.
The timeline has health officials considering other options, including Merck’s Ebola vaccine, called Ervebo.
Ervebo targets the Zaire strain, the most common and deadly type of Ebola.
Some animal studies suggest Ervebo may offer some protection against the Bundibugyo virus – although Ebola experts say existing data is limited and more research is needed.
“This is not a vaccine for Bundibugyo,” Moorthy said Wednesday, adding that a study to determine whether Ervebo could help mitigate the current outbreak is underway.
A 2011 study published in the Journal of Infectious Diseases found that an early version of Ervebo provided limited protection against Bundibugyo virus in macaques. Three in four vaccinated animals survived exposure to Bundibugyo, compared to 1 in 3 unvaccinated animals, although all vaccinated macaques developed symptoms.
Since some macaques might have survived without the vaccine, the protection offered by the vaccine could be lower, closer to 50%, said Tom Geisbert, a subject expert on Ebola for the WHO and author of the 2011 study.
“It’s a toss-up,” Geisbert said. “Unfortunately, these non-human primate studies…they’re just not large and you don’t have the statistical power.”
Until now, global health officials had not seen a need for a Bundibugyo vaccine, said Dr. Geeta Sood, a hospital epidemiologist at Johns Hopkins Bayview Medical Center.
Previous outbreaks of the Bundibugyo virus were small, Sood said, rare and relatively easy to contain.
Bundibugyo virus has a mortality rate of about 25 to 40 percent, she said, lower than other types of Ebola, which average around 50 to 60 percent.
Without a vaccine, public health officials are returning “pretty much to the basics of Ebola,” said Alan Gonzalez, deputy director of operations for Médecins Sans Frontières, “which is contact tracing and identification, safe isolation of patients, the ability to implement infection prevention and control in all the places we work.”