We Might Be on the Verge of an Ebola Vaccine That Works

A Canadian-made Ebola vaccine developed at rapid speed and tested in West Africa has proven 100 percent effective so far, leading officials to call it a potential silver bullet.

"We believe that the world is on the verge of an efficacious Ebola vaccine," doctor Marie Paule Kieny, an assistant director-general at the World Health Organization, said at a press conference Friday.

The vaccine, developed by researchers at Canada's National Microbiology Lab in Winnipeg, was tested on nearly 4,400 people in Guinea.

The researchers' strategy was to vaccinate neighbors, friends, and family of recently-identified Ebola patients, forming a ring of protection around the primary patient, Kieny explained. This would protect the contacts of the patient and prevent the disease from spreading further. The same strategy, called "ring vaccination," was used in the 1970s to successfully eradicate Small-Pox, she said.

Each ring of contacts was randomized to either be vaccinated immediately, or vaccinated after three weeks, and then the two groups were compared to determine whether the vaccine worked.

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The trial is still ongoing, but the data so far shows that none of the 2,014 people who were vaccinated immediately developed Ebola after 10 days of vaccination. The 10-day period is key since some contacts who had already incubated the virus before that time may still have developed the disease, even if they immediately received the vaccine.

Of the 2,380 people in the control group who received the vaccine after three weeks, 16 developed Ebola.

The confidence interval for the study was between 75 and 100, Kieny said, so it is likely that the true result lies between 75 and 100 percent.

However, she noted, there are currently very few Ebola cases in Guinea, so it is difficult to test the vaccine on additional rings to see further results. Researchers have decided to stop randomized trials on each ring, instead vaccinating everyone immediately. The next step is also to vaccinate teenagers and children, which wasn't done before due to lack of data on the vaccine's safety, she said.

"So we hope that by continuing the trial with this modification, with doing all the vaccination immediately, and also including younger people, we will be able to assist the Ebola response team, bringing Ebola transmission to zero in Guinea," Kieny said Friday.

Related: 'We Are Laying Down Like Dogs': The Long Wait For Ebola Treatment in Liberia 

The vaccine could potentially bring the largest Ebola outbreak in history to an end. The number of cases of Ebola in Guinea, Liberia, and Sierra Leone has totaled 27,748 cases as of July 26. Over 11,000 people have died in the West African nations.

"This new vaccine, if the results hold up, may be the silver bullet against Ebola, helping to bring the current outbreak to zero and to control future outbreaks of this kind," the foreign minister of Norway Børge Brende said Friday. Norway helped fund the trial.

According to the World Health Organization, the Ebola outbreak appears to be slowing down. A July 29 situation report showed seven confirmed cases of Ebola in the week up to July 26, which is the lowest weekly total in over a year.

But the deadly outbreak isn't over yet. The WHO points to recent high risk events in Sierra Leone and Guinea, although it says no new cases have been reported in Liberia.

Follow Hilary Beaumont on Twitter: @hilarybeaumont

Watch the VICE News Documentary, The Fight Against Ebola here: