14 September 2018 Vol 361, Issue 6407
Steep drop in Zika cases undermines vaccine trial
By Jon Cohen
Science14 Sep 2018 : 1055-1056 Restricted Access
Controversial strategy of intentionally infecting volunteers to test vaccine candidates is now back on the agenda.
When Zika raced through the Americas in 2016, it caused widespread alarm because the usually mild infection led to brain damage in babies. An intense effort began to develop a Zika vaccine, and in March 2017, the U.S. National Institute of Allergy and Infectious Diseases launched a $110 million trial of its most promising candidate. The trial, now taking place in nine countries in North and South America, has hit a wall: There are too few cases of Zika in the region—largely because vast swaths of populations were infected and now are immune—to assess whether the vaccine works. As a result, researchers are now planning to vaccinate people and then intentionally infect them with the Zika virus. This human challenge model, used for decades with other diseases, was dismissed as too risky by an ethics committee just last year, mainly because infected people can sexually transmit the virus to people who are not in the study. But given the drop in transmission, a better understanding about the duration of sexual transmission, and decreasing interest from industry in Zika vaccine R&D, the human challenge model now looks like the best way to move the field forward.