Pfizer, Moderna and Novavax have made it clear that they need time to make tens of millions of doses of the shots that would be available in the fall.

“I think that’s what today’s discussion is about — how to best to come up with what goes into people’s arms to offer the best protection during a period when we think we’ll have waning immunity,” said Dr. Peter Marks, the F.D.A.’s vaccine chief. He added that the winter may also bring “further evolution of the virus.”

Since the beginning of the pandemic, 6.2 million hospitalizations and 1.1 million deaths have been attributed to the virus in the United States, according to data presented by Natalie Thornburg, a vaccine expert at the Centers for Disease Control and Prevention.

She said the picture had improved this year, but those who remain vulnerable include the unvaccinated, people who are immunocompromised and those who have diabetes or chronic kidney, lung, cardiovascular or neurologic diseases. People 65 and older are also at risk, and that rises with age.

The bivalent shots offered last fall included protection against the Omicron variant and an early Covid variant. About 20 percent of adults, or about 53 million, in the United States got the booster shot, with the rates higher among older adults.

Moving ahead with a shot targeted at only an XBB variant means that newborns and people with compromised immune systems may not have immunity against the earliest coronavirus variants. That should not be a problem, according to a briefing given by a World Health Organization official, who said those variants were no longer in circulation.

The F.D.A. is expected to make a more official recommendation to vaccine makers soon. The manufacturers will be expected to study the new formulas and submit data to the agency. If approvals are granted, the C.D.C. will advise health providers on which age groups should get the jab.

An F.D.A. spokesman said it expected that an updated vaccine would be available by late September, assuming the data support safe and effective vaccines.

It remains unclear whether or when the vaccine makers or the F.D.A. will examine the potential effects of administering multiple vaccines in the fall, including those for the flu and respiratory syncytial virus, or R.S.V., which are expected to be available for pregnant people and older adults. Agency advisers have also endorsed the use of an R.S.V. antibody shot to protect infants.

Leave a Reply

Your email address will not be published. Required fields are marked *