The research available so far on how well the vaccines prevent transmission is preliminary but promising. “We feel confident that there’s a reduction,” said Natalie Dean, a biostatistician at the University of Florida. “We don’t know the exact magnitude, but it’s not 100 percent.”

Still, even an 80 percent drop in transmissibility might be enough for immunized people to toss their masks, experts said — especially once a majority of the population is inoculated, and as rates of cases, hospitalizations and deaths plummet.

But most Americans are still unvaccinated, and more than 1,500 people are dying every day. So given the uncertainty around transmission, even people who are immunized must continue to protect others by wearing masks, experts said.

“They should wear masks until we actually prove that vaccines prevent transmission,” said Dr. Anthony S. Fauci, director of the National Institute for Allergy and Infectious Diseases.