Ebola vaccine proves successful in clinical trial

THE current outbreak of Ebola fever, in Guinea, Liberia and Sierra Leone, which has killed more than 11,000 people, has dropped out of the news as it has been brought under control. But, though new cases are now measured in dozens, rather than hundreds, a week, the disease has not been stamped out—and a new epidemic could flare up somewhere else at any time. A vaccine against the virus responsible would be of enormous value. And a paper just published in the Lancet suggests one is now available.

This vaccine, developed by the Public Health Agency of Canada, and called rVSV-ZEBOV, smuggles one of the Ebola virus’s coat proteins into a person’s body in a Trojan horse called a vesicular stomatitis virus. This is a horse and cattle virus, and does not cause human illness, but its presence is enough to activate the immune system. This then learns to recognise and react to the Ebola coat protein—and thus, the vaccine’s inventors hope, to clobber Ebola, should it arrive in the vaccinated person’s body.

The trial that the Lancet reports was conducted on more than 7,600 people in Guinea by a group of researchers led by Marie Paule Kieny of the World Health Organisation and John-Arne Rottingen of the Norwegian Institute of Public Health. It involved a procedure called ring vaccination, in which clusters of people who were particularly at risk were offered the chance to be vaccinated. A cluster included everyone who had been in contact with a confirmed case of Ebola, and everyone who had in turn been in contact with one of these people. Most adults in each cluster were eligible for vaccination (the exceptions were women who were pregnant or breast-feeding) and the majority volunteered. Each cluster was assigned, at random, to one of two groups, known as arms. Those in one arm were offered the vaccine immediately. Those in the other were offered it after a three-week delay.

Ebola’s incubation period is ten days, and no one who had been vaccinated in either arm of the trial contracted the disease once that ten-day period was up. In the case of those in the arm in which vaccination was delayed, there were 16 cases between the moment ten days had elapsed and the moment, 11 days later, when participants were vaccinated. The vaccine, in other words, worked with 100% efficiency as far as those enrolled in the trial were concerned.

In light of this, though trials continue, every new cluster involved will receive the vaccine immediately. If it continues to prove efficacious, approval for general use will no doubt follow, and its use will spread to the other two infected countries, permitting the epidemic to be ended once and for all.