WASHINGTON — With a stockpile of at least 100 million doses at the ready, Biden administration officials are developing a plan to start offering coronavirus booster shots to some Americans as early as this fall even as researchers continue to hotly debate whether extra shots are needed, according to people familiar with the effort.
The first boosters are likely to go to nursing home residents and health care workers, followed by other older people who were near the front of the line when vaccinations began late last year. Officials envision giving people the same vaccine they originally received. They have discussed starting the effort in October but have not settled on a timetable.
While many outside experts argue there is no proof yet that the vaccines’ protection against severe disease and hospitalization is waning in the United States, administration officials say they cannot afford to put off figuring out the logistics of providing boosters to millions of people until that tipping point is reached. The spotty nature of the nation’s disease-reporting network makes the question of timing even trickier.
The effort comes as yet another wave of the coronavirus grips the nation, reversing much of the progress the administration had made. Hospitals in states like Texas, Louisiana and Mississippi are again swamped with patients, the vast majority of them unvaccinated.
Among other indicators, officials say, the administration is carefully watching Israel, where some data suggests an uptick in severe disease among older adults who received the Pfizer-BioNTech vaccine early in that nation’s campaign, according to people who have reviewed it. Some officials are concerned that even if a decline in protection merely results in mild or asymptomatic infections, those infected people could still spread the virus and prolong the pandemic.
Any booster policy decision is fraught, officials said, because the administration does not want to undermine public confidence in what have proved to be powerfully effective vaccines. Nor does it want to overvaccinate Americans when many other countries have yet to even begin vaccination campaigns in earnest, increasing the threat of dangerous new variants that could spread to the United States and evade the vaccines.
The World Health Organization has called for a moratorium on booster shots until the end of September, saying available doses should be used to help countries that are far behind in vaccinations.
Regulators for the European Union said this month that there was not yet enough data to justify boosters. Germany and France nevertheless have announced plans to start giving booster shots to the older adults and other vulnerable populations next month.
Israel, which is already administering booster shots to people over 60, announced on Thursday that it would offer them to those over 50 as well. Britain so far is holding off, but already has a detailed plan for distributing boosters to people 50 and over.
More than a million Americans have already managed to get booster shots, even though the Food and Drug Administration has not even been asked to rule on whether they are safe or effective.
They represent fewer than 1 percent of those who have been fully vaccinated. But more people could try to follow suit once regulators fully approve the Pfizer-BioNTech vaccine, a move that is expected by early next month. Even though the regimen calls for two shots, doctors would be able to prescribe a third for patients at that point without fear of violating F.D.A. rules.
Late this week, the F.D.A. authorized third doses of the Pfizer and Moderna vaccines for certain people with weakened immune systems and the C.D.C. recommended them. The authorities decided those individuals, who make up fewer than 3 percent of Americans, merited extra shots because many fail to respond to the standard dosage.
Administration officials continued to insist that boosters remained unnecessary for the general population for now. Determining at what point that changes is difficult because administration experts lack up-to-date data on so-called breakthrough infections in vaccinated people, including their prevalence, when such people were vaccinated and which vaccine they received.
Instead, officials are analyzing a complex array of information from a range of sources, including from the vaccine manufacturers Moderna and Pfizer-BioNTech, which has an agreement with the Israeli government to review its data. Other sources of information include a variety of foreign governments, and the Centers for Disease Control and Prevention, which collects data from states and hospitals. All of that data is subject to interpretation and can be marshaled to support arguments for or against boosters.
“It’s somewhat chaotic, with everybody doing their own thing,” said Dr. Jesse L. Goodman, a former chief scientist at the F.D.A. and now a medical professor at Georgetown University. “We need a system to monitor real-world vaccine effectiveness in near-real-world time.”
He added: “When something comes up like the Pfizer report on Israel, we should be able to say, ‘Are we seeing that here?’ I’m very distressed that we’re not there yet.”
Some federal officials cast the booster discussions as contingency planning; others suggested boosters for the general population were extremely likely and the questions were how to give it to them and when.
Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases and a key White House adviser, said on Thursday that officials were busy planning because “sooner or later you will need a booster.”
Jeff Zients, the White House coronavirus coordinator, said that if and when extra shots were needed, they would be rolled out “in a fast and efficient way.”
Vaccine makers, who run multibillion-dollar businesses, have been among the most vocal proponents of boosters.
“Countries will have to decide either to be two months too early or two months too late,” Stéphane Bancel, the chief executive of Moderna, said in an interview on Monday. While the decision is up to public health authorities, he said, “Our recommendation would be to be two months too early because we can save lives and prevent hospitalization.”
On the other side are some influential scientists who say booster shots are at best premature and at worst unethical absent convincing real-world evidence showing that the effectiveness of the vaccines against severe disease and hospitalization is waning.
“Vaccinate the unvaccinated, vaccinate the world, and then talk about boosters,” said Dr. Luciana L. Borio, a former acting chief scientist at the Food and Drug Administration.
According to the C.D.C., only a tiny fraction of the more than 166 million fully vaccinated Americans have been hospitalized for Covid-19 or have died. Of that number — 8,054 as of Aug. 9 — three-fourths were 65 or older. But the agency says the true total is likely larger because the data relies on voluntary reporting from the states.
Data from Israel has prompted growing concern. With only 8.7 million residents, Israel has outpaced the United States in vaccinating its population. It has relied almost exclusively on the Pfizer-BioNTech vaccine and has a nationalized health care system that allows it to systematically track patients.
Researchers at Israel’s Ministry of Health have said that the Pfizer vaccine’s effectiveness in preventing infection fell from 95 percent early in the year to 39 percent from late June to mid-July. The vaccine’s overall efficacy against severe disease remained high, though, at 91.4 percent.
More recent Israeli data suggests continued erosion. One person who has reviewed it said it showed that the Pfizer vaccine’s efficacy against severe disease had dropped significantly for those 65 and older who got their first shots in January or February.
Moderna officials reported in an earnings call last week that six months after a person received their second dose, the strength of their antibodies against variants was found to have waned substantially. But many scientists say that waning antibodies are expected and should not be viewed as a sign that a vaccine is working less well.
In general, U.S. scientists are frustrated with how bits and pieces of often conflicting data are dribbling out in company news releases and studies that have not been peer-reviewed or published in scientific journals.
The C.D.C. has said it is following breakthrough infections in specific population segments, including health care workers, emergency medical workers and nursing home residents. But the reports posted on its website rely on data from months ago, before the Delta variant became dominant.
“Everyone is confused because there is not a lot of published data,” Dr. Peter J. Hotez, a vaccine expert with the Baylor College of Medicine in Houston, said. “The question is how vulnerable are we, and the numbers are a bit all over the map.”
While some federal officials have argued that any booster should be tailored to the Delta variant, the administration is expected to use the same vaccines that have already been manufactured and that studies indicate work well against the Delta variant.
Mr. Bancel, Moderna’s chief executive, said his company would not have a vaccine targeted specifically to the Delta variant until the end of the year. Pfizer is on a similar track.
Both companies are expected to apply soon to the F.D.A. for authorization of a third shot of their existing two-dose vaccines. Moderna is studying the effectiveness of both a full dose and half dose as a booster.
N.I.H. researchers are conducting trials to determine if giving people a booster shot of a different vaccine from the one they originally received provides better protection. While a mix-and-match effort could be hard to organize, officials want to see that data.
“It’s a little compressed from what you would normally want,” said Dr. John Beigel, who is leading the study. “But we want to make sure we have data to inform decisions this fall.”
Benjamin Mueller contributed reporting from London, and Noah Weiland from Washington. Kitty Bennett contributed research.