The FDA released the findings Wednesday in a report analyzing data submitted by Pfizer Inc. and BioNTech SE as part of their request for authorization for their vaccine to be given as a booster shot in people 16 years and older.

An outside panel of scientific advisers will review the FDA report on Friday, along with a companion analysis from Pfizer and other information, as part of a discussion over who needs booster shots and when.

The Biden administration had targeted next week to start widely distributing the extra shots to counter contagious variants such as Delta and bolster signs of waning immunity among the vaccinated. Evidence supporting the need for an extra dose, at least in the general public, hasn’t been conclusive.

The booster campaign hinges on FDA clearance of the additional shots and input by the panel meeting on Friday, plus a separate committee of outside experts that advises the Centers for Disease Control and Prevention. The CDC recommends who gets priority for the vaccines and when.

A favorable recommendation from the panel to authorize boosters for the general population could be followed within a few days by the FDA approving distribution of booster shots of the vaccine.

The findings the FDA released on Wednesday could complicate that decision. One possible outcome would be for the panel to recommend booster shots for now to only certain groups, such as healthcare workers or people 65 and older, according to people familiar with the matter.

White House press secretary Jen Psaki said Wednesday that the data would inform the deliberations of the panels advising the FDA and the CDC. The CDC committee, which will meet next week to discuss boosters, last month expressed preliminary support for booster doses, specifically for groups at high-risk for severe disease and death.

FDA scientists wrote Wednesday that they considered concerns that recent studies that show diminished levels of antibodies and weaker protection against symptomatic Covid-19 may result in additional severe disease, and that the highly contagious Delta variant has further spread the virus.

Yet they expressed skepticism that an apparent diminished protection is rendering the vaccines less effective. Some observational studies have suggested Pfizer-BioNTech’s vaccine, over time, offers less protection against symptomatic disease or against Delta, while others haven’t.

“Overall, data indicate that currently U.S.-licensed or authorized Covid-19 vaccines still afford protection against severe Covid-19 disease and death in the United States,” the scientists wrote.

The FDA’s assessment appeared to indicate it might not endorse a widespread booster campaign for now, while Pfizer’s briefing report said such an approach is necessary because of data from Israel and other sources indicating that vaccine efficacy is waning.

Israeli researchers will present data on Friday to the panel making the case for boosters, which some senior U.S. officials have cited to support additional doses. The Israeli data, released Wednesday in the New England Journal of Medicine, showed that rates of infection and severe illness were substantially lower among study participants aged 60 and over who had been vaccinated at least five months earlier and then received a booster dose of the Pfizer vaccine.

The FDA reviewed data submitted by Pfizer on more than 300 subjects from its clinical trial who received a third dose of the shot. The data showed significant increases in neutralizing antibodies, which are important in the immune response to stopping Covid-19.

No new serious safety concerns were found in people who received the booster shots, the FDA said, and reported side effects such as fatigue or fevers were similar to what was previously reported in trial subjects. The agency said that Pfizer’s analysis of a third dose met its criteria for a safe and effective vaccine.

It isn’t known if there will be an increased risk of myocarditis, an inflammatory heart condition, or other adverse reactions after a booster dose of the Pfizer-BioNTech vaccine, the FDA wrote.

The FDA in August fully approved the Pfizer-BioNTech vaccine, which is marketed under the name Comirnaty, for people 16 years and older.

The FDA released its report on Wednesday, two days ahead of a meeting of the Vaccines and Related Biological Products Advisory Committee, an advisory panel that will decide whether to recommend Americans receive booster shots.

The FDA isn’t required to accept any decision by the panel but generally does. Panel members include infectious-disease experts, professors and practicing physicians.

Gregory Poland, director of the Mayo Clinic’s vaccine research group, said deciding whether to expand boosters for the general population should be based on more data than what was presented Wednesday, including the more than 300 people Pfizer cited.

“To me this is insufficient evidence to support a national booster program,” said Dr. Poland, a former VRBPAC member.

Federal officials in August recommended that adults who received a two-dose regimen of mRNA vaccines such as Pfizer’s begin receiving booster shots this month. Officials said at the time that the shots would be administered about eight months after the second dose for people ages 18 and older. The Wall Street Journal has reported that officials are likely to approve a booster shot starting at least six months afterward.

The timetable could still be pushed back, at least for Moderna Inc. and Johnson & Johnson, makers of the other vaccines cleared by regulators in the U.S.

Pfizer and Moderna have submitted data to the FDA for authorization of booster shots, while J&J is expected to do so soon.

Moderna released an analysis of clinical trial data on Wednesday that the company said showed a lower risk of breakthrough infections in more recently vaccinated participants than participants who were vaccinated last year. The company said the findings add support to the case for a booster dose of its vaccine. Moderna’s president, Stephen Hoge, said a third dose could extend immunity through next year.

Health authorities have already authorized booster shots for people 12 years old and above whose immune systems are compromised.

People 65 and older and individuals in chronic-care facilities are expected to get extra shots first, along with healthcare workers and anyone else who was vaccinated earliest, according to federal health officials.

An extra dose of a vaccine mobilizes the body’s immune system defenses further to protect against Covid-19, especially variants such as Delta. Pfizer and BioNTech said early testing indicates a booster shot given at least six months after the second vaccine dose produces antibody levels five to 10 times higher than after two doses.

A late-stage trial last year of more than 44,000 people found that two doses of the vaccine were more than 95% effective at preventing symptomatic Covid-19. Data from Pfizer indicates its vaccine is still highly effective in people six months after their second dose, but that its protection diminishes by around 6% every two months after the second dose.

In its briefing document, Pfizer said “the totality of the available data supports the public health need” for an additional dose about six months after the second one. The company cited real-world data from Israel and the U.S. that suggested declining protection is due more to waning effectiveness than the impact of the Delta variant.

The FDA noted in its own briefing document that the decision to approve a booster authorization should consider whether current dosing courses work against variants.

At the FDA’s request, Pfizer submitted data showing how a booster would fare against the Delta variant. In 11 subjects between ages 18 and 55 who received a booster, neutralizing antibodies were fivefold higher one month later, compared with one month after their second shot, the data showed. In 12 older subjects, the increase was 12-fold.

The Biden administration and drug companies have said that there should be enough supply for the boosters if distribution begins more widely this month. The U.S. has purchased a combined one billion doses from Pfizer and Moderna.

This story has been published from a wire agency feed without modifications to the text