Given the limited number of vaccines available to states and the logistical hurdles to distribution, including the fact that two doses are needed several weeks apart, experts said that vaccinating the nation’s three million schoolteachers could be a slow process, taking well into the spring.

And even once enough educators are inoculated for school officials and teachers’ unions — which hold considerable power in many large districts — to consider it safe to reopen classrooms, schools will likely need to continue requiring masks and distancing students for many months, experts said, until community spread has sharply dropped, possibly by summer.

“I think some people have in their head that we’re going to start rolling out the vaccine and all this other stuff is going to go away,” said Marcus Plescia, the chief medical officer at the Association of State and Territorial Health Officials, which represents public health agencies.