WASHINGTON >> Top federal health officials have told the White House to scale back a plan to offer coronavirus booster shots to the general public later this month, saying that regulators need more time to collect and review all the necessary data, according to people familiar with the discussion.

Dr. Janet Woodcock, acting commissioner of the Food and Drug Administration, and Dr. Rochelle Walensky, who heads the Centers for Disease Control and Prevention, warned the White House on Thursday that their agencies may be able to determine in the coming weeks whether to recommend boosters only for recipients of the Pfizer-BioNTech vaccine — and possibly just some of them to start.

The two health leaders made their argument in a meeting with Jeffrey Zients, the White House pandemic coordinator. Several people who heard about the session said it was unclear how Zients responded. But he has insisted for months that the White House will always follow the advice of government scientists, wherever it leads.

Asked about the meeting, a White House spokesperson today said, “We always said we would follow the science, and this is all part of a process that is now underway,” adding that the administration was awaiting a “full review and approval” of booster shots by the FDA as well as a recommendation from the CDC.

“When that approval and recommendation are made,” the spokesperson, Chris Meagher, said, “we will be ready to implement the plan our nation’s top doctors developed so that we are staying ahead of this virus.”

Less than three weeks ago, President Joe Biden said that, contingent on FDA approval, the government planned to start offering boosters the week of Sept. 20 to adults who had received their second shot of the Pfizer-BioNTech or Moderna vaccine at least eight months ago. That would include many health care workers and nursing home residents as well as some people older than 65, who were generally the first to be vaccinated. Administration officials have said that recipients of the single-dose Johnson & Johnson vaccine would probably be offered an additional shot soon as well.

Biden cast the strategy as another tool that the nation needed to battle the highly contagious delta variant, which has driven up infection rates, swamped hospitals with COVID-19 patients and is now leading to an average of more than 1,500 deaths a day. “The plan is for every adult to get a booster shot eight months after you got your second shot,” he said Aug. 18. “It will make you safer, and for longer. And it will help us end the pandemic faster.”

Like Biden, members of his pandemic response team have said that the plan depended on the FDA and the CDC authorizing the booster shots. Both Woodcock and Walensky publicly endorsed the strategy, as did the nation’s other senior health leaders.

Privately, Woodcock had argued that it was risky to set a firm date for a booster rollout before regulators had a chance to thoroughly review the data, some of which had yet to be submitted by the vaccine manufacturers, and decide whether shots were safe and necessary, according to several people familiar with the discussions.

And since the White House announced the booster plan in mid-August, they said, new hurdles appeared.

Among the reasons for delaying is that regulators need more time to decide the proper dosage for a possible third Moderna shot. The company’s application asking the FDA to authorize a booster shot contains insufficient data, one federal official familiar with the process said. Other data expected from Johnson & Johnson has not been delivered.

Nor has the raw data that the FDA has been seeking from Israel, which is already giving boosters to everyone 12 and older. Israeli officials say their data shows that the potency of Pfizer’s vaccine wanes over time against severe disease and hospitalization but that a third shot bolsters protection significantly. The FDA wants to see the underlying data to make sure it backs up summaries that the Israeli government has provided.

Narrowing the booster plan could confuse the public and create a perception that federal vaccine policy is in some degree of disarray. But some public health experts will most likely welcome it.

They have been arguing strenuously that the administration lacks the data to justify a broad rollout of extra shots and should instead concentrate on vaccinating the roughly 25% of Americans who are eligible for shots but remain unprotected. And some have said that Biden aides wrongly cornered regulators by announcing a strategy before they could conduct a full review.

Regulators are only beginning to review critical data that will help them determine if and how boosters should be given. Pfizer completed its booster application to the FDA last week, officials said, and Moderna has just initiated its own.

This week, two of the FDA’s top vaccine regulators announced that they would be leaving the agency this fall, apparently partly because of frustration with the administration’s booster plan. Dr. Marion Gruber, who directs the agency’s vaccines office, and her deputy, Dr. Philip Krause, have told people there was not nearly enough data to justify offering extra shots to the general population starting in just weeks.

More friction may lie ahead. On Sept. 17, the FDA’s outside advisory committee is scheduled to publicly review Pfizer’s data supporting a booster shot. Even though Pfizer has asked the FDA to approve booster doses for people 16 and older, the agency could decide to restrict who gets a booster. The CDC and its outside advisory panel would also have to weigh in.

One key member of the FDA’s advisory panel, Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, argues boosters are premature. “There is no compelling reason to get a third dose” now, he said in an interview Thursday.

He said the administration had appeared to expect that the FDA and the CDC would rubber-stamp its booster timeline. “Bypassing and marginalizing those agencies led veterans who you need in this pandemic to leave the FDA,” he said, referring to the departures of Gruber and Krause.

Various studies have shown that the potency of the Pfizer-BioNTech and Moderna vaccines ebbs against infection over time but suggest that the vaccines continue to offer robust protection against severe illness and hospitalization.

But Dr. Vivek Murthy, the surgeon general, said in an interview Thursday that a few studies have suggested a dip in protection against severe disease over time. “Our feeling was that if we waited several more months, we would see protection against hospitalizations and deaths break down,” he said.

In an interview published Thursday on WebMD.com, Woodcock echoed that view, saying that the trend of breakthrough infections has led health officials to believe at some point “we are going to see hospitalizations and more serious disease” among fully vaccinated people. When that happens, she said, “we want to be ready” with the booster plan.

Some Americans are already getting booster shots before FDA approval: More than 1 million fully vaccinated people have received an additional dose since mid-August.

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