Experimental Ebola Vaccine Gives 100 Percent Protection in Trial

An unusual trial design helped prove the vaccine safe and effective in less than a year

Stop Ebola
An actor, playing the role of a vaccine against Ebola, performs at a school in Abidja, Ivory Coast, last September LUC GNAGO/Reuters/Corbis

At least 11,294 people have died and 27,784 have been infected with Ebola in the 18-month long epidemic still affecting West Africa, according to the World Health Organization. But today there is good news in the fight against Ebola: a study shows that starting ten days after a single shot of newly-developed vaccine, recipients have 100 percent protection against the virus.

"This will go down in history as one of those hallmark public health efforts," says Michael Osterholm, the director of the Center for Infectious Disease Research and Policy in Twin Cities, Minnesota, in a Science story by Martin Enserink. "We will teach about this in public health schools."

The vaccine, produced by Merck and first developed at the Public Health Agency of Canada, went through a clinical trial in Guinea between April and July of this year.

The trial’s design was unconventional. Most vaccines going through testing rely on a standard randomized controlled trial, where half a population at risk would get a vaccine and half would get a placebo. However, the current outbreak’s waning cases meant that researchers didn’t have enough people for such a trial. Instead, they used a "ring" design for the trial: when Ebola appeared in a village, all people in contact with the sick person received the vaccine. To test how well the vaccine worked, each cluster was randomly assigned to immediate vaccination or vaccination 21 days after Ebola was confirmed. Researchers used a similar method to test smallpox vaccines in the 1970s, reports Sarah Boseley for The Guardian.

Of the 2,014 people who received the vaccine immediately, every one was protected from the virus. Sixteen people of the 2,380 who were vaccinated later contracted the virus. The research team reported the results in the journal Lancet

"With such high efficacy, all affected countries should immediately start and multiply ring vaccinations to break chains of transmission and vaccinate all frontline workers to protect them," says Bertrand Draguez, the medical director for Médecins sans Frontières, according to James Gallagher for BBC News

Typically, testing new vaccines takes years, if not a decade. Scientists decided to advance this vaccine to trial last October. The trial will still continue in Guinea, where any person who develops Ebola, and their contacts, will be offered the vaccine. With larger numbers of people, the researchers suspect that the eventual efficacy numbers for the vaccine will fall between 75 and 100 percent.

The next step is for regulatory agencies to approve the vaccine for stockpiling, in the event of future Ebola epidemics, reports Boseley for The Guardian. Public health officials are now calling for the vaccine to be given to people in Sierra Leone as well, in the hopes that it can quash the ongoing outbreak still claiming lives there.

But while the vaccine's success has been greeted the world over with relief, a vaccine doesn’t spell the end of worry over Ebola. Vaccinating every single person will be a massive challenge — and Ebola outbreaks are very unpredictable in terms of where and when they start, explains Olga Khazan in a story last year for The Atlantic. A treatment that works even if Ebola has taken hold would be better. 

However, given the relatively small number of people who die from Ebola (compared to killers like malaria and tuberculosis), funding is tight for the disease. That’s why the World Health Organization itself needed to back the new vaccine — even as the search for an effective treatment lags behind.

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