Agency leaders said there was evidence to justify approval only for older people and those with medical conditions. Many others may not be able to get the shots.

By Christina Jewett and Apoorva Mandavilli, NYT

The Food and Drug Administration will permit Covid vaccines for adults over 65 and those with certain medical conditions in the fall, according to new regulatory standards detailed on Tuesday by agency officials.

But the F.D.A. may require data from additional clinical trials before approving the vaccines for healthy Americans younger than 65, agency officials wrote in The New England Journal of Medicine.

New doses offer “uncertain” benefit to many Americans under 65 who have previously been vaccinated or have had Covid, Dr. Vinay Prasad, the F.D.A.’s vaccine division chief, and Dr. Martin Makary, the agency’s commissioner, wrote.

Citing low uptake of recent Covid shots, “the American people, along with many health care providers, remain unconvinced” that the shots are needed, the officials said.

During the pandemic, both officials sharply criticized vaccine mandates and other public health measures intended to turn back the coronavirus.

“The F.D.A. will approve vaccines for high-risk persons and, at the same time, demand robust, gold-standard data on persons at low risk,” Dr. Prasad and Dr. Makary wrote.

Robert F. Kennedy Jr., the health secretary, is a prominent vaccine skeptic who spent years campaigning against the Covid shots.

More on Covid-19

• Efforts to Thwart mRNA Therapies: The therapies, a key to Covid vaccines, hold great potential in treating several diseases, but some lawmakers want to ban them and the government is cutting funding. We asked experts about how the technology works, its safety and its potential in medicine.
• Vaccine Approvals: Health Secretary Robert F. Kennedy Jr. announced plans to require all new vaccines to be tested against placebos and to develop new vaccines without using mRNA technology, moves that raise questions about whether Covid boosters will be available in the fall.
• Gut Issues: Why does Covid cause diarrhea, constipation, pain and bloating? Here are some suggestions for what to do about these conditions.
• Heart Problems: One recent study found that a Covid infection doubled the risk of a major cardiovascular event for up to three years afterward. People who had severe infections were especially vulnerable.
• Paxlovid and Long Covid: A new report suggested the drug might improve symptoms for some patients, but results were mixed.
• Retracing Covid’s Origins: Researchers contend that the Covid pandemic got its start from bats, which jumped to wild mammals in China that were taken by wildlife traders.

Under his leadership, the Department of Health and Human Services has taken a more critical view of vaccines in general, raising questions about their safety and whether they should be so widely administered.

The officials are expected to expand on the agency’s recommendations Tuesday afternoon. Scientific advisers to the agency are set to meet Thursday to decide how the fall Covid shots should be composed.

Before approving Covid vaccines, the F.D.A. “anticipates the need” for new data from clinical trials in which participants under 65 are randomly assigned to receive the new shots, the officials said.

Pfizer and Moderna, makers of the most widely used Covid vaccines, did not immediately comment.

Some experts said the new criteria go too far, erecting barriers for people who will want the shots.

“This is overly restrictive and will deny many people who want to be vaccinated a vaccine,” Dr. Anna Durbin, director of the Center for Immunization Research at Johns Hopkins University, said in an email.

The changes do “not make sense from a public health perspective,” she said.

Some experts said that while they agreed with aspects of the new rationale, the new restrictions would unnecessarily limit access for healthy Americans who may be at high risk because of their occupation or for other reasons.

“Since the public trust in vaccines has declined, I would hope that we would be thoughtful about preserving vaccine choice for people who want to get vaccinated,” said Dr. Denise Jamieson, vice president for medical affairs at the University of Iowa and an adviser on immunizations to the Centers for Disease Control and Prevention.

This “doesn’t preserve people’s choice to get vaccinated,” she added.

The new recommendations mark a departure from the previous policy of offering annual Covid shots to everyone 6 months and older, the “most aggressive” strategy when compared with other nations, the F.D.A. officials noted.

“We simply don’t know whether a healthy 52-year-old woman with a normal B.M.I. who has had Covid-19 three times and has received six previous doses of a Covid-19 vaccine will benefit from the seventh dose,” they wrote.

Other high-income nations have long adopted “risk-based” recommendations targeting the shots to those most in need.

The new process could upend insurance and public coverage of Covid vaccines, experts said. And the officials did not address some reasons healthy people seek the vaccine, such as to protect a loved one or inoculate a child who has not had Covid nor the shot. Children under 4 remain at high risk from Covid.

Federal agencies already have robust data showing that Covid vaccines offer modest protection against hospitalization and death even at younger ages, some scientists noted.

“We need to also include the role of observational data and the role of the C.D.C. in continuously monitoring vaccine safety and efficacy,” Dr. Jamieson said. “We have a lot of accumulated data at this point.”

It is the C.D.C. that usually defines who should get a vaccine and when, based on guidelines set by a panel of external advisers. “C.D.C. is the agency that really has the expertise in that area,” Dr. Jamieson said.

It is unclear how the new criteria will affect availability of Covid vaccines in the fall. The World Health Organization has said that the mRNA Covid vaccines offered last fall are suitable to use this year.

The proposed regulations align with the agency’s recent decision to narrow the eligibility for the Novavax Covid vaccine.

The F.D.A. on Friday approved that shot for use only in adults over 65 and for others over age 12 who have at least one medical condition that puts them at high risk should they contract Covid.

The decision was met with some criticism, given the absence of new evidence to suggest concerns about the effectiveness or side effects. It “does seems to be based more on this administration’s hostility to vaccines and resentment of Covid prevention methods,” Dr. Durbin, of Johns Hopkins, said.

“I think this is setting a dangerous precedent,” she added.

The officials said the F.D.A. would rely on results from lab tests to show that the vaccine still provides valuable protection to Americans older than 65 and for those older than 6 months who have one or more risk factors for severe outcomes, as defined by the C.D.C.

The list of risk factors is long, including asthma, diabetes, “physical inactivity” and mental health conditions like depression. The F.D.A. officials estimated that 33 percent of Americans would be eligible for the vaccine.

But Dr. Jamieson said that estimate seemed too low, adding that a majority of Americans had risk factors.

This developing story will be updated.