The Centers for Disease Control and Prevention’s independent committee of vaccine experts has scheduled a meeting for Friday to discuss data on the booster dose’s efficacy and safety. If both the F.D.A. and the C.D.C. sign off this week, they will have acted strikingly quickly — a little more than a week after Pfizer asked for authorization of boosters for everyone 18 and older.

Under that scenario, any adult who received a second dose of the vaccine at least six months earlier would be officially eligible to get a booster as soon as this weekend. The F.D.A. is expected to rule without consulting its own expert panel, which has met frequently during the pandemic to review vaccine data and make a recommendation ahead of a regulatory decision.

The broad booster authorization has been viewed as something of a fait accompli for weeks. Some state and local officials have begun rolling out similar policies ahead of F.D.A. action — responding to persistent virus case counts, including some breakthrough cases, and the eagerness of many Americans to seek additional protection ahead of holiday gatherings.