• The Food and Drug Administration outlined new regulatory guidance for future Covid-19 vaccine boosters, setting stricter approval standards for healthy Americans. 
• The FDA recommended different standards of evidence for approval based on patients' risk of getting severely sick from Covid.
• The agency said it wants to see new clinical trials showing Covid shots are still safe and effective before approving them for healthy adults and children, a costly new requirement for pharmaceutical companies that could potentially limit who gets new jabs each year.

The Food and Drug Administration on Tuesday outlined new regulatory guidance for future Covid-19 vaccine boosters, setting stricter approval standards for healthy Americans. 

The agency said it wants to see new clinical trials showing Covid shots are still safe and effective before approving them for healthy adults and children, a costly new requirement for pharmaceutical companies that could limit who gets new jabs each year. Previously, the FDA typically approved updated Covid shots for all Americans each year based on simple tests that show they trigger a strong enough antibody response.

"The truth is that for most of that, for many Americans, we simply do not know the answer to whether or not they should be getting the seven or eight or nine or ten, as the current policy would have us" do, said Vinay Prasad, an outspoken critic of the pharmaceutical industry who was appointed to lead the agency's division that oversees vaccines, during a town hall on Tuesday.

The FDA recommended different standards of evidence for approval based on patients' risk of getting severely sick from Covid, according to a paper published Tuesday in the New England Journal of Medicine. The paper's authors are FDA Commissioner Marty Makary and Prasad.

"The FDA's new Covid-19 philosophy represents a balance of regulatory flexibility and a commitment to gold-standard science," the agency said in the paper. "The FDA will approve vaccines for high-risk persons and, at the same time, demand robust, gold-standard data on persons at low risk.

Covid vaccine makers such as , its partner and may see slightly lower revenue if the new guidelines are implemented broadly, BMO Capital Markets analyst Evan Seigerman said in a note on Tuesday. But overall, Seigerman said he views the guidelines as "fair and considerate" of the benefits and risks healthy people may gain from additional vaccinations.

"We appreciate new appointees do not appear to be overreaching in their generalizations on Covid-19 vaccine efficacy," he said.

Jefferies analyst Michael Yee, who covers Moderna, said the new regulatory guidelines "seem OK for now." The framework is "generally expected" and in line with commentary from advisors to the Centers Disease Control and Prevention leaning toward risk-based vaccine recommendations rather than a universal one.

"So in the big picture this actually eases some investor concern for 2025 guidance to some extent," Yee said.

But Yee said it's unclear if the clinical trials requirement will apply for next-generation Covid shots or combination vaccines targeting Covid and other viruses, such as the flu.

The new guidance comes as Health and Human Services Secretary Robert F. Kennedy Jr., a prominent vaccine skeptic, overhauls the nation's health agencies and U.S. immunization policy.

For adults 65 and older, and for people as young as 6 months who have certain underlying health conditions, the FDA said it will accept immunogenicity data — which shows a vaccine generates a strong immune response — as enough to determine that a shot's benefits outweigh its risks. The FDA estimates that 100 to 200 million Americans have conditions that put them at high risk of severe illness, including obesity and mental health conditions such as depression.

"There will be a quick regulatory path for such products to come to market" for that age group, Prasad said during the town hall.

But for healthy people between 6 months and 64 years old who don't have risk factors, the FDA plans to require stronger evidence for vaccines from randomized, placebo-controlled trials. That means some people would receive the actual shot while others get an inactive substance like a saline shot, to compare results.

The main goal of the trials should be showing that the shots help prevent symptomatic Covid, with data showing at least 30% effectiveness, according to the paper. People who've had Covid in the past should still be included in the trial to better reflect the general population, the paper said.

Drugmakers will need to track participants for at least six months "to ensure that early booster gains persist," they added.

"Our policy also balances the need for evidence," Makary and Prasad wrote in the paper. "We simply don't know whether a healthy 52-year-old woman with a normal BMI who has had Covid-19 three times and has received six previous doses of a Covid-19 vaccine will benefit from the seventh dose."

The FDA said that when it approves a Covid vaccine for high-risk people, it will encourage manufacturers to conduct randomized, controlled clinical trials in healthy adults as part of their post-marketing commitment for the shot.

During the town hall, Prasad suggested annual updates to Covid vaccinations may not be necessary, saying that the virus is "mutating at a slower rate" than the influenza. He said he expects the FDA to require randomized clinical trials for Covid boosters every few years or "however long that may be" rather than studies every year.

"The virus doesn't have a calendar," he said, adding, "Why don't we let the science tell us when we should change" shots to adapt to a major shift in the virus.

FDA rejects 'one-size-fits-all' approach

The paper argued that the nation's "one-size-fits-all" Covid vaccine policy approach, which recommends annual shots for all Americans above six months old, is outdated and no longer in line with other countries. All other high-income nations limit vaccine recommendations to older adults or those at high risk for severe illness due to Covid, the paper said. 

The paper said the benefit of repeat vaccinations is "uncertain," particularly among low-risk patients who have developed some immune protection through previous shots, infections or both. The paper said many Americans and health-care providers "remain unconvinced" of that benefit, pointing to data from the Centers for Disease Control and Prevention on falling vaccination rates in the U.S. for annual Covid boosters. 

The paper cited CDC data that indicates that for the past two seasons, fewer than 25% of Americans have received a Covid-19 shot, including fewer than 10% of kids and fewer than 50% of adults over the age of 75. Less than one-third of health-care workers received updated Covid boosters in the 2023 to 2024 season, the paper said, citing CDC .

The paper also suggested that broad Covid vaccine recommendations each year have contributed to declining trust in vaccination, including in the measles-mumps-rubella vaccine. Still, the paper called MMR vaccines "clearly established as safe and highly effective."