The C.D.C.’s gathering on Friday is scheduled to be briefer than recent meetings about Covid vaccines — just three hours. It is expected to be straightforward, one federal official familiar with the planning said, in part because of how far the nation’s booster campaign has already come. That would suggest a significant softening of opposition among public health experts since President Biden announced in August that he hoped to offer booster doses to all adults.
Mr. Biden wanted to start the campaign in late September, but his announcement was heavily criticized by public health experts, who said he was rushing the federal scientists and regulators responsible for deciding whether the data supported such a move.
Some key regulators and outside advisers had argued that the effectiveness of the two-dose regimen, especially in preventing hospitalization and death, has held up strongly. One large study in New York of nearly nine million people has shown remarkable durability in the protection gained from all three federally authorized vaccines.
But more recently, some federal regulators and scientists have said the evidence is increasingly clear that a reduction in vaccine efficacy against milder Covid cases, and in protective antibodies, has put Americans — especially seniors and those with medical conditions — at risk of harmful breakthrough infections as the Delta variant of the virus only gradually loosens its grip.
Pfizer and BioNTech said last week that their request is based on data from a clinical trial in the United States and elsewhere that included more than 10,000 volunteers. After a third dose, the vaccine’s efficacy rate against symptomatic disease had been restored to about 95 percent, they said. It remains unclear, however, how long the protection from a booster shot will last.
Moderna is expected to soon submit its own request for the F.D.A. to broaden eligibility for its booster. But for now, every adult can get the Pfizer booster if it is broadly authorized, according to people familiar with the planning.
Top federal health officials, including Dr. Anthony S. Fauci, have argued for months — often pointing to Israel, which started its booster campaign in late July and now offers extra shots to everyone 12 and older — that the case for boosting widely in the United States is clear. Dr. Fauci said at an event sponsored by Reuters on Tuesday that the virus could potentially be brought under control in the U.S. by the spring if boosters were available for everyone.