Who Will Get the Coronavirus Vaccine First?

Three companies have announced preliminary data indicating their vaccines are effective, and there are dozens of additional candidates in clinical trials. Can I choose which vaccine I get?

This depends on a number of factors, including the supply in your area at the time you’re vaccinated and whether certain vaccines are found to be more effective in certain populations, such as older adults. At first, the only choice is likely to be Pfizer’s vaccine, assuming it is approved. Moderna asked the F.D.A. for emergency authorization on Monday; if approved, it would most likely become available within weeks after Pfizer’s.

Are there any side effects from the shot?

Some participants in both Pfizer’s and Moderna’s trials have said they experienced symptoms including fever, muscle aches, bad headaches and fatigue after receiving the shots, but the side effects generally did not last more than a day. Still, preliminary data suggests that, compared with most flu vaccines, the coronavirus shots have a somewhat higher rate of such reactions, which are almost always normal signs that the body’s immune response is kicking in. At the meeting of the C.D.C. advisory committee last week, some members said it would be important for doctors to warn their patients about possible side effects and assure them of the vaccines’ safety.

How do I know it’s safe?

Each company’s application to the F.D.A. includes two months of follow-up safety data from Phase 3 of clinical trials conducted by universities and other independent bodies. In that phase, tens of thousands of volunteers get a vaccine and wait to see if they become infected, compared with others who receive a placebo. By September, Pfizer’s trial had 44,000 participants; no serious safety concerns have been reported.

The F.D.A. will also review the data for each vaccine seeking authorization and share it with its advisory committee, which will meet publicly — in the case of the Pfizer vaccine, on Dec. 10 — to ask questions and make a recommendation to the agency. The F.D.A. will then decide whether to approve the vaccine for emergency use.

I had Covid-19 already. Do I need the vaccine?

Probably. Although people who have contracted the virus do have immunity, it is too soon to know how long it lasts. So for now, it makes sense for them to get the shot. The question is when.

Some members of the C.D.C. advisory committee have suggested Covid survivors should be toward the back of the line.

“At the beginning, when it’s a resource-limited vaccine, my opinion is that we need to try and target as best we can to those that we know are susceptible,” Dr. Robert Atmar, an infectious disease specialist at Baylor College of Medicine who serves on the committee, said during a meeting of the panel last week.

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