Highly-Effective Ebola Vaccine Could Stymie Future Outbreaks

Over 27,000 cases and 11561 deaths. The statistics that tell the story of the most recent Ebola outbreak are stark, but a new number published today in the medical journal The Lancet may be even more significant.

One-hundred percent effective.

That’s the conclusion of a study on an Ebola vaccine developed in a 10-month sprint by the Public Health Agency of Canada and the Merck Pharmaceuticals and quickly pressed into clinical trials. Though preliminary, the results of this phase III clinical trial, which involved over 7,000 individuals in Guinea, are welcome news.

Kimberley Steeds in the ebola vaccine lab at Donka Hospital in Conakry, Guinea
Kimberley Steeds, an Ebola vaccine trial team member, in the Ebola vaccine laboratory, Donka Hospital in Conakry, Guinea

“This is an extremely promising development,” Margaret Chen, director general of the World Health Organization, said in a statement.

The vaccine is consists of a modified version of a different virus called VSV, which infects cows and deer but is nonthreatening to human health. Researchers forced VSV to express a protein found on the surface of Ebola virus, making it a kind of sheep in wolf’s clothing. When injected into humans, our immune system mounts a response to the modified VSV virus and, in doing so, learns to recognize the Ebola protein—but the patient doesn’t get sick. Later, if the real Ebola virus enters the body, the immune system recognizes and fights off the threat.

The trials employed the same strategy used to contain smallpox called “ring vaccination.” When a person comes down with the disease, health workers identify and vaccinate anyone likely to come in contact with the patient, creating a ring of protection that hopefully keeps the virus contained and prevents it from spreading.

The new study evaluated the vaccine’s effectiveness by dividing recipients into two randomly assigned groups. Half of the study participants received the vaccine as soon as one person they had been in contact with—whether it was a relative, patient, or someone else—had been diagnosed with Ebola. The other half received the vaccine after a delay of three weeks. In the 2,000 subjects receiving the immediate vaccination treatment, not one person contracted Ebola. Based on these results, the immediate vaccination regimen was offered to all participants starting on July 26. Even with the vaccine’s apparent efficacy, the trial will continue so researchers can gather more information to license the vaccine for widespread use.

The study was orchestrated by a partnership including the WHO, the Ministry of Health of Guinea, Doctors Without Borders, and many others, comprising a monumental scientific and logistical effort. Here’s James Gallagher, reporting for the BBC:

The sheer scale of the 2014-15 outbreak led to an unprecedented push on vaccines – and a decade’s work has been condensed into around 10 months.

The numbers of Ebola outbreak cannot be erased, but the vaccine trials offer, for the first time, hope that such grim statistics will never be seen again.