The Food and Drug Administration’s independent panel on vaccines voted Friday to recommend booster shots of the Pfizer-BioNTech COVID-19 vaccine to Americans 65 years of age and older, and those at risk of severe disease. 

The vote comes after an earlier vote, where they decided to not recommend booster shots of the Pfizer-BioNTech COVID-19 vaccine for most Americans.

The vote on widespread booster availability came as a major blow to President Joe Biden, who announced last month that the U.S. would start offering booster shots of the Pfizer and Moderna vaccines the week of Sept. 20 to people eight months after their initial vaccination was completed, pending approval from federal regulators. The decision undercuts the Biden administration’s sweeping effort to shore up nearly all Americans’ protection amid the spread of the highly contagious delta variant.

Some health experts accused Biden of exerting pressure on regulators by announcing his booster plan before they were able to formally review the data.

In the first vote, members cited a lack of safety data on extra doses and also raised doubts about the value of mass boosters, rather than ones targeted to specific groups.

Following the first vote, the panel revised the question to vote on whether to authorize a booster of the Pfizer-BioNTech COVID-19 vaccine for adults 65 and older and those at risk for severe disease. The subsequent vote was unanimous.

“Today the VRBPAC reviewed data from our clinical program showing a favorable safety profile and strong immune responses against SARS-CoV-2 after a booster dose of our vaccine," Kathrin Jansen, senior vice president and head of vaccine research and development at Pfizer, said in a statement to Spectrum News. "These data, and the larger body of scientific evidence presented at the meeting, underscore our belief that boosters will be a critical tool in the ongoing effort to control the spread of this virus. We thank the committee for their thoughtful review of the data and will work with the FDA following today’s meeting to address the committee’s questions, as we continue to believe in the benefits of a booster dose for a broader population.”

Separate FDA and CDC decisions will be needed in order for people who received the Moderna or Johnson & Johnson shots to get boosters.

Pfizer asked the FDA to amend approval of its two-shot vaccine to include an additional booster dose for people 16 years and older six months after they were given their second shot. The drugmaker said studies show the vaccine’s effectiveness wanes over time. 

Entering the meeting, there was plenty of debate among the medical community about whether booster shots are necessary.

A big question that seemed to be facing committee members is whether a booster should be approved if the vaccines remain highly effective in preventing severe illness and death, even though the number of breakthrough infections might be one the rise.

Addressing the panel early in the day were CDC scientist Dr. Sara Oliver; British statistician Jonathan Sterne, who co-wrote an article in a medical journal opposing booster shots now; and health officials in Israel, which in late July became the first country to begin administering the additional vaccine doses.

One question committee members seemed to be focused on was whether data showing vaccines have become less effective over time were the result of waning potency, a result of the emergence of the highly transmissible delta variant or a combination of the two. 

“It's difficult to distinguish the effects of increased time since primary series (of vaccinations) versus the impact of the delta variant,” Oliver acknowledged at the end of her presentation.

The Israeli officials said that they are seeing waning immunity there in severe disease in people ages 60 and older and that the same could soon be true for younger age groups as well.

They cited a study that found that, as of April, the two-dose Pfizer vaccine was 97% effective in preventing severe cases in people who were inoculated from January to March. In July, the shots were 85% effective in individuals vaccinated in January. While 85% might still seem like a high number, that 12-percentage-point decline could translate to a five-fold increase in severe cases, the officials said.

An Israeli model projected that, based on the level that cases had been rising, hospitalizations could have significantly exceeded the national capacity if the country had not launched its booster campaign when it did, the officials said.

“If we had not started booster doses, at the end of July we would have come to the capacity of the hospitalization capabilities and probably have gone beyond,” said Dr. Sharon Alroy-Preis, director of public health services at the Israeli Health Ministry. 

Another factor to consider was the potential for cases of myocarditis in younger people who are given booster shots. This summer, the FDA added a warning to Pfizer’s and Moderna’s vaccines about mild, rare cases of heart inflammation seen in some teens and young adults following vaccinations.

In giving instructions to the committee at the start of the meeting, Dr. Marion Gruber, the FDA’s director of the Office of Vaccines Research and Review, said members were to weigh the benefits of a booster shot versus the risks, and she noted that little is known about myocarditis related to the third shots.

The Israeli officials said one case of potential myocarditis has been reported out of the 2.8 million booster shots administered there. They, however, noted that because older people were given priority in the rollout, most younger people have only received their booster shots in the last two weeks. 

When asked if Israel had any concerns about myocarditis before it approved boosters, Alroy-Preis said that scientists know the risk of developing the heart inflammation is higher in people infected by COVID-19 than it is from receiving the vaccine. She added that the vast majority of myocarditis cases related to vaccines has been mild.

The Israeli officials said studies have found that the vaccine was 95% effective against infection, even against delta — similar to the level of protection seen initially after the second shots were given. They added that no new side effects were found and that the rate of adverse events was lower than seen with earlier doses.

With the U.S. looking to Israel as a case study on boosters, committee member Dr. Michael Kurilla of the National Institutes of Health asked the Israeli officials if they believed boosters might be needed every six months.

“I think it's not really clear where this is going,” Alroy-Preis said. “We definitely don't have any plans at the moment to boost every six months. We'll base it exactly as we did here, based on the results. We'll continue to monitor and see if there is again any waning effect, but it may be that we won't see that, that after the booster, we’ll have a higher protection for a longer period of time.”

She added that boosters shots have resulted in protection for years from certain viruses, including hepatitis.

Some critics, including World Health Organization head Tedros Adhanom Ghebreyesus, have argued against COVID-19 booster shots, saying administering them now would contribute to vaccination inequity between wealthier and poorer countries.

Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, however, instructed the committee members Friday not to take that matter into consideration.

"As we proceed, I would ask that we do our best to focus our deliberations on the science related to the application under consideration today, and not on operational issues related to a booster campaign or on issues related to global vaccine equity,” Marks said. “If we stray into those latter topics, the chair and I will gently bring us back into the scope of this advisory committee meeting.”

Earlier this week, the FDA released data Pfizer presented to the agency trying to make the case that boosters are needed now.

Pfizer said clinical trials found that the vaccine’s efficacy dropped roughly 6 percentage points every two months, the company said.

The vaccine maker also said its own analysis found that the rate of breakthrough cases — infections of fully vaccinated people — was higher among those who received their second dose at least eight months prior to July 1 compared to four months earlier. Pfizer said the analysis was performed in July and August, as the delta variant was raging.

The FDA granted full approval to the Pfizer-BioNTech vaccine last month, but booster shots require separate authorization. Boosters, however, are currently available in the U.S. to immunocompromised people.

On Monday, the medical journal The Lancet published an opinion piece by an international group of scientists, including the statistician Sterne, who argue that the average person doesn’t need a COVID-19 booster yet.

The experts reviewed studies of the vaccines’ performance and concluded the shots are working well despite the extra-contagious delta variant, especially against severe disease.

The authors also include two FDA officials — Gruber and her deputy, Dr. Philip Krause — who recently announced they will be stepping down this fall.

Moderna submitted its application for booster approval Sept. 3. The FDA has not yet announced a meeting to discuss its request, but Friday's vote likely dooms its prospects as well.

The Associated Press contributed to this report.