Cases of Zika have plummeted to levels so low that most people vaccinated in the trial likely will never be exposed to the virus, which could make it impossible to tell whether the vaccine works.

“Right now, there are no infections, and certainly not enough to even think about an efficacy signal at this point,” says Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Maryland, which launched the trial. Human trials of other Zika vaccine candidates at earlier stages are also in limbo, and last year one large vaccinemaker pulled the plug on development of its candidate. But NIAID and others are pressing ahead, saying a vaccine might someday be needed. To make up for the lack of new cases, other investigators are turning to an unusual, and ethically complex, strategy. Starting next year, Science has learned, they plan to test a vaccine by deliberately infecting people with Zika.

Launched in March 2017, NIAID’s placebo-controlled vaccine trial includes two sites in Brazil, where Zika hit hardest and where the brain damage known as microcephaly first surfaced. From the beginning of the outbreak in 2015 until the start of this year, Brazil had about half of all 800,000 suspected and confirmed Zika cases in the Americas, according to the Pan American Health Organization in Washington, D.C. But from January through June, Brazil’s Ministry of Health reported fewer than 7000 probable cases, in a nation of 200 million people. “It’s a good dilemma because we don’t have Zika anymore,” says Esper Kallás of the University of São Paulo in São Paulo, Brazil, principal investigator for the local NIAID site. “But it’s a dilemma. Everybody is concerned about it. It’s a lot of investment.”

…continue reading ‘As massive Zika vaccine trial struggles, researchers revive plan to intentionally infect humans’

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