WASHINGTON — Anxious about a surge of coronavirus infections enveloping Europe as cases tick up in the United States, senior health officials in the Biden administration are pressing urgently to offer vaccine booster shots to all adults. But support for the renewed push is not unanimous.

Centers for Disease Control and Prevention Director Rochelle Walensky has expressed caution about making extra shots so broadly available now, according to several officials familiar with the situation who spoke on the condition of anonymity to discuss internal deliberations. As a result, tension is rising among officials over how quickly to proceed and who should get the shots.

The debate comes at a critical time for the Biden administration, with top advisers growing increasingly fearful the country could slide backward into a fifth pandemic wave amid colder weather and declining vaccine protection. Eager for the president to push his economic agenda, many aides see expanding booster access as a way to backstop progress against the highly transmissible delta variant. Allies also see defeating the pandemic as critical to Democrats' success in next year's midterm elections.

The debate over booster eligibility centers on a request by Pfizer and its partner BioNTech to the Food and Drug Administration to authorize the shots for everyone 18 and older who has gone at least six months since completing their vaccine regimen. If the FDA grants the request, CDC's outside vaccine advisers would most likely need to weigh in before Walensky makes a final decision.

In a meeting Sunday with high-ranking health officials, Walensky said that she and the advisers want to scrutinize the drug companies' data and might not agree to such a broad recommendation, said an official close to her who spoke on the condition of anonymity to describe a private meeting. It's extremely rare for the CDC to overrule the recommendations of its advisers.

"She wants to see the data so she can formulate her decision," the person said, referring to Pfizer's most recent request to FDA. "Someone took that as her reservation. That's not her reservation. She was pointing out that they might not go along. She knows no matter what, the decision is hers."

Walensky's skittishness reflects the attitude of some CDC officials and advisers who are not convinced young, healthy people need additional protection, especially since the Pfizer-BioNTech and Moderna vaccines have been linked to a rare cardiac side effect in male teenagers and young men. They also note that focusing on boosters may distract front-line personnel from the more critical effort to defeat the pandemic, which is to get unvaccinated people their first shots.

Walensky declined to comment on internal deliberations about the boosters. "CDC officials will await FDA regulatory action before announcing next steps," CDC spokesperson Kristen Nordlund said this week in response to questions.

Most of the administration's senior health officials — including Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases; Surgeon General Vivek Murthy and David Kessler, chief science officer of the White House COVID-19 response team — are strong supporters of booster shots for all adults, according to people familiar with their views. Murthy did not respond for a request for comment and Kessler declined to comment.

Fauci said in an interview that he backs wider access to boosters "given that we are starting to see plateauing and even in certain states, an actual increase in cases." He added, "I have always been and still am in favor of boosters. Exactly who gets the boosters is up to the FDA and up to the CDC."

Many supporters of expanded eligibility and front-line health-care personnel believe the current recommendations are confusing and discourage people from getting the shots, even if they might be eligible. CDC recommendations say that people are eligible if they are at least 65 years old, or at high risk because of medical conditions or exposure at work or in living situations.

They also point to mounting evidence that the vaccines' protection wanes over time. And with breakthrough infections occurring nearly a year after the vaccines were first authorized, some officials are frustrated by Walensky's hesitation, saying there is no time to lose to curb the virus' spread.

"Europe is on fire," said a senior health official. "And in the United States, the case counts are not going down. States in the Midwest are getting redder" with rising rates of COVID-19, the illness caused by the virus.

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The FDA, which is reviewing the companies' data, plans to conduct an in-depth risk-benefit analysis before making a final decision on the request. The agency is strongly inclined to grant it, perhaps by the end of the month — though a disagreement with the CDC could complicate matters.

For example, if the agencies disagree on whether all adults should be eligible, they might hammer out a compromise that would clear the boosters for people 30 and older, under one scenario.

Paul Offit, a vaccine expert at Children's Hospital of Philadelphia and a member of the FDA's vaccine advisory panel, said the decision on whether young people should receive a booster hinges on whether the benefits to males 18- to 29-years-old "clearly and definitively outweigh the risk" of myocarditis, a rare inflammation of the heart muscle linked to the vaccines.

"All the evidence is that they are protected against serious illness," if they are fully vaccinated, he said, even if protection wanes against breakthrough infections. Offit voted against boosters for all adults in September, as part of the FDA advisory panel.

But a senior Biden administration official was critical of that viewpoint. "Those who are aware of the totality of evidence are confident that the benefits outweigh the risks in the overall adult population," the official said.

Some state officials aren't waiting for Washington to act. California state officials, worried about a potential rise in cases, on Wednesday urged all adults who are six months past vaccination to get a booster. In Colorado, where a surge of COVID-related hospitalizations is putting severe stress on the health care system, state officials unilaterally declared this week that everyone over 18 was eligible for a booster if they waited the specified time after being vaccinated, and ordered pharmacists not to deny anyone.

A growing number of countries, including Canada and Germany have authorized booster shots for all adults; Israel has cleared them for people 12 and over. But the debate in the U.S. has been heated from the start. In mid-August, senior administration health officials announced they believed all adults would need boosters, in part because of Israeli data showing waning protection. They said they planned to make those extra doses available beginning the week of Sept. 20, assuming sign-off from the FDA and CDC.

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But in September, outside vaccine advisers to those agencies balked at making the Pfizer-BioNTech booster available to all adults, saying there was insufficient evidence, and the agencies backed off. The FDA authorized boosters for the eligibility categories now being used. Shortly afterward, the CDC's immunization advisers voted against recommending the shot for people at risk of contracting the virus on the job.

Walensky, in a rare move, overruled them on that issue. Some administration officials say Walensky does not want to be put in that uncomfortable position again, should the outside experts reject a blanket booster recommendation for adults.

In non-pandemic times, it's not unusual for CDC to make a more limited recommendation than the FDA. But in a public health emergency, it could be confusing to the public if the two agencies are not in sync, according to officials.

Some administration officials already are concerned that the public debate over the boosters over the last few months, especially the disagreements voiced by the agencies' advisers, has made it harder to convey the urgency of getting extra protection.

Their worries have intensified as new daily infections cases have ticked up to a seven-day average of 76,000 on Wednesday — the last day of full reporting because of Veterans Day — after hitting a low of about 69,000 new cases a day in late October, while continuing to claim more than 1,200 lives a day.

This time round, the FDA has indicated it does not plan to take the boosters-for-all issue to its outside advisory committee. The agency has discretion on when to consult the advisers.

Meanwhile, some officials at the CDC, which takes the lead in recommending how vaccines should be used, have suggested that other officials appear to pressuring the agency to make a decision it views as premature.

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Supporters of broad eligibility argue that authorizing boosters for all adults would simply be an explicit recognition of what is already occurring: Many people are getting access to the shots by saying they are in an eligible group since pharmacies are using the honor system. They say it's time to get rid of rules that lead people to pretend they are immunocompromised or work in a hospital.

Some states are taking matters into their own hands: Colorado Gov. Jared Polis, D, issued an executive order Wednesday declaring the entire state of Colorado "high risk for exposure or transmission of COVID-19 for the purpose of COVID-19 booster shot eligibility." The decision to expand eligibility beyond high-risk groups was driven by soaring virus transmission and modeling that showed increasing the shots could preserve capacity at hospitals that are already dangerously full.

Rachel Herlihy, Colorado's state epidemiologist, said that with the current rollout of boosters based on age and other risk factors, the hospitalizations would peak on January 1 with 2,258 people hospitalized. If, instead, three-quarters of people over 18 receive boosters by the end of the year, the peak is projected to occur about two weeks earlier, peaking with 2,082 people in the hospital.

"We can potentially at our peak avoid several hundred hospitalizations, and that … could mean the difference for us here in Colorado between exceeding and not exceeding our hospital bed capacity," Herlihy said.

The Washington Post’s Carolyn Y. Johnson and Jacqueline Dupree contributed to this report.