The idea, known as a “challenge trial,” would deliberately infect a few hundred young, healthy volunteers, who were first given either the potential vaccine or a placebo. Those picked would be well informed about the risks.

That would allow the effectiveness of a vaccine to be determined faster than a traditional clinical trial, which would require that researchers wait for some of the participants to become infected in the course of their daily lives.

Supporters say the challenge trial could save several months in the search for a vaccine, which is widely seen as critical for people to feel confident again with social gatherings.