Advisers to the US Food and Drug Administration have begun debating whether to recommend authorising Pfizer’s application to offer widespread booster doses of its Covid-19 vaccine.

Members of the regulator’s vaccine advisory committee are expected to vote at the end of Friday’s meeting on whether to endorse a third dose of the BioNTech/Pfizer vaccine. While the Biden administration has already announced plans to launch a booster programme next week, some health officials have pushed back.

Marion Gruber, the director of the FDA’s office of vaccine review, is one of two senior officials to have spoken out against the plan, arguing that there is insufficient data to show that the effectiveness of two vaccine doses wanes over time. Gruber is retiring from the FDA next month, and allies have said she is unhappy at the way in which the regulator has been undermined by other parts of the Biden administration.

Speaking at the beginning of Friday’s meeting, Gruber stressed the high bar for recommending approval. “There’s an expectation that demonstration of the effectiveness of the additional dose is based on adequate and well-controlled clinical trials,” she said.

“The available data to support the effectiveness of a booster dose — specifically against currently circulating Sars-Cov-2 variants — and the benefit of the booster dose should be considered relative to the benefit already provided by previous vaccinations with the primary series.”

Sara Oliver, a scientist at the Centers for Disease Control and Prevention’s division of viral diseases, said: “Protection against infection . . . [is] lower in recent months. However, it is difficult to distinguish the effects of increased time since primary series versus the impact of the Delta variant.”

Pfizer is seeking authorisation to offer people aged 16 and older a booster of its two-dose messenger RNA jab at least six months after receiving the second shot. US regulators could choose to limit the availability of booster doses only to over-65s, a significantly narrower plan than that outlined by the White House a month ago.

Andy Slavitt, a former Covid adviser to US president Joe Biden, told the Financial Times: “The CDC may decide to say we recommend this for over-65s, but it is up to patients to discuss with their physicians whether to get a booster dose.”

If the committee recommends approving the application, the FDA is likely to give its final sign-off within days. Once the CDC has issued guidelines for who should be eligible, Americans should be able to start getting booster jabs next week.

Earlier this week, Pfizer and Moderna both released data suggesting the effectiveness of their mRNA vaccines can decline within months after a second shot.

Data from Israel show severe Covid cases began to decline sharply about 10 days after the booster programme started. Covid cases there jumped more than 10-fold from early July to August, with 60 per cent of cases in fully vaccinated people, data from the country showed.

“If we had not started booster doses at the end of July we would have come to the capacity of the Israel hospitalisation capability and probably gone beyond it,” Sharon Elroy-Preiss, director of public health services at Israel’s health ministry, told the panel on Friday.

The FDA has already authorised booster shots of mRNA vaccines for people with weakened immune systems. But the idea of allowing booster shots more broadly is controversial, both because of the limited data available about the vaccines’ long-term effectiveness in the real world, and because many countries are still struggling to secure initial supplies.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, has backed broad distribution of booster shots. He told the committee on Friday that they should focus “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.”

In a report published on Wednesday, FDA staff said the data were not conclusive on whether the vaccine’s ability to stop symptomatic infection declined significantly over time, a sign of internal frictions within the regulator about whether boosters are needed.

“Overall, data indicate that currently US-licensed or authorised Covid-19 vaccines still afford protection against severe Covid-19 disease and death in the United States,” the briefing document said.

Others argue that US regulators should act quickly to stem the recent rise in coronavirus cases.

Ali Mokdad, professor of global health at University of Washington, said: “We need to get a booster for everyone and to move on. Once we have boosters out then we can donate vaccines.”

In an open letter published on Thursday ahead of the FDA meeting, Pfizer’s chief executive Albert Bourla said allowing people in rich countries to get boosters would not divert supplies from those in need.

“If the data demonstrates their need, safety, and efficacy then they should be approved . . . I believe, however, that the introduction of booster doses should not change the number of doses that each country receives,” he wrote.