President Biden vowed to “follow the science” in fighting the coronavirus pandemic, but some scientists say his decision to recommend widespread coronavirus vaccine booster shots relies on incomplete data and will put pressure on regulators yet to approve the plan.

The Biden administration’s decision to order up booster shots for vaccinated adults “doesn’t make any sense to me at all,” said Vincent Racaniello, a professor of microbiology and immunology at Columbia University. “I think it’s way premature because the science doesn’t say that we need to have a booster right now. It could be a year or two, depending on the data.”

The White House announced Wednesday that every adult American should make plans to get a booster shot, arguing that a third dose of coronavirus vaccine would boost protection against the delta variant as well as new variants that might arise. While Biden acknowledged the plan was “pending approval” from the Food and Drug Administration and experts who advise the Centers for Disease Control and Prevention, the president mostly portrayed it as a done deal, saying that tens of millions of booster shots would become available the week of Sept. 20.

“Just remember, as a simple rule. … Eight months after your second shot, get a booster shot,” Biden said.

The president’s top science and medical advisers — including senior CDC and FDA officials — concluded last weekend that widespread booster shots were necessary, drawing on an array of data from the United States and Israel that suggested immunity from a two-dose regimen of coronavirus vaccine declined over time and that greater protection might be needed against the highly contagious delta variant. The Biden administration has spent more than a month planning for the possibility of booster shots, including securing hundreds of millions of additional doses in June and July.

Senior officials defended announcing the booster-shot plan before regulators could approve it, saying the virus’s fast spread and continued evolution were forcing a more-rapid response. Coronavirus infections have surged more than tenfold since early July, from about 13,000 new infections per day to nearly 140,000 now, according to The Washington Post’s rolling seven-day average. Most of those are among unvaccinated people, but a growing number are “breakthrough” infections among the fully vaccinated, including three U.S. senators who announced their positive tests Thursday.

“We’ve learned over and over again: If you wait until you see real trouble starting, you’ve waited too late. We want to be a step ahead of it,” said Francis Collins, director of the National Institutes for Health.

Biden's decision also was hailed by some health officials who are set to execute it on the ground.

“I think it is good to have a month to plan,” said Claire Hannan, executive director of the Association of Immunization Managers, which helps organize vaccination campaigns across the United States. “There’s a lot of coordination needed to implement the booster dose for all adults,” including updating storage protocols, scheduling systems and vaccine availability.

But a number of outside experts faulted Biden’s timing and said the White House was acting prematurely based on the latest vaccination data.

For instance, the administration focused on multiple research studies showing that vaccine effectiveness against mild to moderate illness wanes over time, while boosters ramp up antibodies tenfold or more. Most, although not all, of the recent data shows the vaccines continue to provide robust protection against severe disease.

“Vaccines Effectiveness against Hospitalizations Remains Relatively High,” read three slides presented Wednesday by the White House’s coronavirus task force. One slide showed protection against hospitalization “remained stable at 92%-95%” in a cohort study across the entire state of New York.

Many prominent figures in the scientific and medical communities said that’s the key measure of vaccine success. The vaccines’ main purpose is not to prevent infection, so much as to keep people from getting severely ill or dying, they note, and recent concerns about breakthrough coronavirus infections have been overblown.

“The metric that matters is the protection against severe disease, hospitalization and death among people vaccinated,” said David Rubin, director of PolicyLab at Children’s Hospital of Philadelphia. He said the booster decision was premature and potentially misleading. “It tends to portray that we’ve lost confidence in the ability of this vaccine to prevent severe infection. And I don’t think that’s the case,” he said.

Administration officials counter that they had to make decisions affecting several hundred million people from partial and contradictory data — an effort complicated by the CDC’s failure to provide real-time updates on the U.S. spread. Israeli reports showing rising hospitalizations of vaccinated individuals particularly worried the officials, who want to avoid a similar fate in the United States. The Israeli data indicated the Pfizer vaccine was less than 55 percent effective against serious disease for people 65 and older who were vaccinated in January and February, part of that country’s early vaccination campaign.

Collins said that federal officials are starting to see early signs of that in U.S. data. “It is reassuring that protection against severe illness and hospitalization and death holds up very well for people who are vaccinated, even with Delta circulating,” he said. “But you can see a little bit of a tendency for those numbers to get a little softer.”

Ultimately, senior administration health officials like CDC Director Rochelle Walensky, acting FDA commissioner Janet Woodcock and infectious-disease expert Anthony S. Fauci signed onto a joint statement this week backing the plan, seeking to reassure the public and some agency staff frustrated over what might be seen as a usurpation of regulators’ authority to reach an independent assessment.

Nevertheless, some experts said the White House was backtracking on its pledge to allow regulators to shape coronavirus policy. Both Biden and Vice President Harris criticized President Donald Trump last year for publicly pressuring regulators to approve the first coronavirus vaccines.

Biden officials “got ahead of their skis” by announcing the booster plan, said Holly Fernandez Lynch, a bioethicist and lawyer at the University of Pennsylvania. She and others said the announcement held echoes of the pressure the Trump administration exerted on scientific agencies, like a threat to fire then-FDA Commissioner Stephen Hahn if he didn’t move quickly to approve the Pfizer-BioNTech coronavirus vaccine.

“I didn’t like Trump tweeting at Hahn threatening all those things,” said Fernandez Lynch, adding that “we are clearly seeing pressure” again on the agency now.

Calling for boosters “may be the right decision — let’s see the data — but if it were the _Trump_ administration getting this far out ahead of FDA and CDC on something this significant, there’d be outrage. And appropriately so,” tweeted Jason L. Schwartz, associate professor of health policy at the Yale School of Public Health. “Process matters, no matter which party is in power.”

Administration officials, who spoke on the condition of anonymity to discuss internal deliberations, argued that any delay in outlining their plan would have been unconscionable.

“We’re damned if we do, we’re damned if we don’t,” said one senior administration official. “But the data clearly showed it’s appropriate to recommend booster shots.”

“This is a plan — underline that it is a plan,” subject to FDA and ACIP clearance, another official said. “In a non-pandemic world, there would not be a rush,” but given the swiftly moving delta variant, “this decision is prudent.”

One health official acknowledged that there was “scar tissue” over how the Trump administration had often pressured agencies, but stressed that this year’s process was fundamentally different, noting that the most senior agency heads were involved in the booster decision.

“You don’t want to catch people by surprise, so if your leading public health and scientific officials determine that boosters are needed, you say so,” the official said.

Judgment call on timing

The White House’s decision to recommend booster shots, on one level, was a simple calculation, driven by the fact that vaccine effectiveness against mild to moderate disease has declined — and that still further erosion in protection may occur. But the timing of those shots is a judgment call — a point conceded by Collins, NIH director, discussing the plan to recommend a booster shot eight months after the second dose.

“There’s no magic here about this eight months,” Collins said. “Maybe we could have said seven, maybe we could have said nine. So, let’s try to pick a place that makes sense.”

There is no single point in time when someone who is immunized ceases to be protected. Instead there appears to be a gradual waning of immunity. And there is a question of what is considered an acceptable risk and what requires immediate action.

To make the calculation yet more complicated, the immune system has many distinct elements, a bit like a military that has an Army, Navy, Air Force, Marines and Special Operations units. These include antibodies, “killer” T cells, and “memory B” cells that retain the imprint of previously encountered pathogens (or ones simulated by vaccines) and can put the immune system on a war footing when a person is infected.

“Antibody levels always go down. That’s normal,” Racaniello said. “You’re still protected against serious disease because you have memory, immune memory. The vaccines were never meant to prevent infection.”

Others were cautiously optimistic about the booster-shot timing.

“I took this as a productive example of forward thinking about what we can do to try to stave off even worse trajectories of covid” David Holtgrave, dean of the School of Public Health at the State University of New York at Albany, wrote in an email. “In infectious diseases, you have to stay ahead of the virus at hand; you can’t wait until it has its worst possible impact and then act.”

A former Trump official characterized the administration’s move as overdue, arguing the White House had deferred too much to regulators at the FDA and CDC.

“They waited too long and should have moved as soon as the data from Israel was known,” said Joe Grogan, the Trump administration’s head of domestic policy. Grogan also defended the Trump administration’s effort to shape the regulatory agencies’ response, saying Biden should embrace the tactic.

“You have political leaders leading these agencies, they all report to the president,” Grogan said. “The idea that they should be out there on their own, unresponsive and, frankly, indifferent to the policy imperatives and the national emergency, is absurd. CDC should not be waiting to publish this stuff.”

Decision was weeks in making

Top health advisers to Biden said they have wrestled with the decision for weeks, and chose to recommend boosters before regulators signed off on vaccine makers’ individual applications to ensure there was sufficient time to implement the strategy.

The Trump administration similarly prepared a plan to distribute the first round of vaccines last year before the FDA formally authorized the vaccines, one official said.

Two administration officials also said that government health experts negotiated over whether the booster rollout should begin as soon as mid-September, or be held until October.

State health officials, who will oversee the vaccination efforts, were supportive of the plan.

“It’s always been a question of when, not if,” said Nirav Shah, director of Maine’s CDC and president of the Association of State and Territorial Health Officials. “They [administration officials] went out with the data they had, particularly in light of the fact that folks have called them to task about being slow to respond to emerging data. I can see that as informing their view of being more aggressive here.”

Shah also said it was “very good” to have a target date for the booster rollout.

“We’ve already been planning in the conceptual phase,” he said. “Now we can move from conceptual to tactical.”

Laurie McGinley, Rachel Roubein and Yasmeen Abutaleb contributed to this report.