The scientists leading the trial say it is necessary to prevent a future epidemic. But Ms. Shah and other bioethicists convened by the N.I.H. concluded in 2017 that the research had “insufficient value” to justify the risks.
People outside the study, such as sexual partners, might also be infected, the panel said. And Zika infection might have unspecified consequences for participants in the long term.
But scientists in charge of the study said the panel’s concerns were hypothetical and did not take into account the proposed protocol. They plan to use minimal doses of Zika virus and to quarantine patients in a hospital inpatient unit.
The study also would start by enrolling only women — who are less likely to transmit Zika sexually — and would require them to use long-term birth control.
“It’s really insulting,” said Dr. Stephen Whitehead, a vaccine researcher at the N.I.H., said of the panel’s decision. “We’ve been painted as mad scientists who do horrible studies on human beings. But we’re on top of all these risks.”
Human-challenge studies are only conducted at a small number of institutions in the United States. The trials have been used to test vaccines or treatments for dengue, malaria, influenza and norovirus, among other diseases.
Natural Zika outbreaks are becoming too sporadic to test vaccines, so until the next large outbreak, a human-challenge study may be the only way for vaccine developers to proceed.
“This ethics consultation was debilitating for the whole community,” said Dr. Anna Durbin, a research clinician at Johns Hopkins University who collaborated on the study’s design. “It really slammed the door on progress.”