Safety concerns raised by the pause have discouraged some people who told pollsters they were open to taking a vaccine but wanted to wait and see.

“There is a portion of the population that because of the pause, that’s the straw that broke the camel’s back, they’re not going to get vaccinated.

They just evaporated,” said Paul Shelton, executive vice president of pharmacy at AdhereHealth LLC, a health-technology company that has been operating sites in more hesitant and hard-to-reach populations.