President-elect Joe Biden plans to release nearly all available doses of the coronavirus vaccine once he takes office, seeking to speed up the sluggish start of a mass vaccination campaign as cases soar, hospitals are overwhelmed and a faster-spreading form of the virus has invaded the country.

The plan, announced Friday by the Biden transition team, pivots sharply from the Trump administration’s strategy of holding in reserve roughly half the doses to ensure sufficient supply for people to get a required second shot.

Biden’s plan is the most concrete signal to date of how he intends to reshape the federal role in the unprecedented campaign to vaccinate the nation and tamp down a devastating public health threat. It also places him squarely on one side of a heated dispute over the ethics and practicalities of accomplishing that goal.

“The president-elect believes we must accelerate distribution of the vaccine while continuing to ensure the Americans who need it most get it as soon as possible,” a Biden transition spokesman, T.J. Ducklo, said in a statement. “He believes the government should stop holding back vaccine supply so we can get more shots in Americans’ arms now.”

The announcement came at the end of a grim week, with coronavirus infections, hospitalizations and deaths all reaching record highs. On Friday, new cases surpassed 300,000 for the first time, according to Washington Post tracking, and about 130,000 people were hospitalized. Deaths reported in a single day reached 4,027 on Thursday — the first time the number surpassed 4,000.

The pace of vaccinations amid those worsening numbers has concerned many health officials. As of Thursday, the Centers for Disease Control and Prevention reported, 21.4 million doses had been distributed throughout the country but only 6.6 million of those had been given to people. Federal health officials say the data is incomplete.

The Biden transition team declined to provide details of exactly how much it expects to improve the pace of vaccinations through the release of a much greater share of doses of the vaccines manufactured by Pfizer-Bio­NTech and Moderna, both authorized last month on an emergency basis. Biden previously has set a goal of 100 million vaccinations within his first 100 days in office.

The dispute over whether to reserve doses stems from the fact that the coronavirus vaccines in use require a two-dose regimen to achieve full effectiveness, and the supplies being manufactured are finite and expected to ramp up gradually. To be fully effective, the Pfizer vaccine, the first one approved, requires people who are immunized to return 21 days after a first dose for a second shot, based on data from clinical trials. The Moderna vaccine requires a second dose at 28 days.

The colliding views on reserving doses boil down to a disagreement over how much trust to put in the reliability of the manufacturing of the two vaccines, which rely on a biotechnology never before used for a vaccine. One of the companies, Moderna, is new to vaccine-making.

While officials with the federal Operation Warp Speed vaccine effort have always described the decision to reserve second doses as a temporary strategy, they have not said when they planned to alter it.

A Biden transition official, speaking on the condition of anonymity to reveal greater detail than the public statement, said the Biden team has “faith in our manufacturers that they can produce enough vaccines to ensure people can get their second dose in a timely manner.”

In addition, the official said, the incoming administration will, if necessary, make greater use of the Defense Production Act, a law that gives the government powers to step up manufacturing during wars and other emergencies.

Asked about his vaccine plan at the end of an event Friday in Wilmington, Del., Biden deflected the question, saying he plans to talk about it late next week.

According to Department of Health and Human Services data, Operation Warp Speed is allocating about 2 million Pfizer doses to be distributed next week, holding back an equal amount for second shots, and reserving about 156,000 doses as a safety reserve in case of theft or spoilage.

It is allocating nearly 6 million Moderna doses and holding back an equal amount for second shots next week, with more than 561,000 doses being held in safety reserve.

Vaccinations began in the second half of December, focused primarily on health-care workers and residents and staffers at nursing homes — groups most at risk from covid-19, the illness caused by the virus that, as of Friday, had infected nearly 22 million people nationwide and killed more than 367,000.

The idea of releasing a greater share of vaccine doses has been embraced by a growing cadre of Democrats. Eight Democratic governors dispatched a letter Friday to HHS Secretary Alex Azar and Gustave Perna, chief operating officer for Operation Warp Speed, the Trump administration’s arm created to develop and distribute vaccine in a hurry. The letter, obtained by The Post, says: “Our states and our residents need more vaccines now. This need is all the more urgent with the onset of the new variant of the virus.”

But it is not entirely a partisan idea. At a meeting of the White House coronavirus task force Tuesday, some of the physician members suggested that the government was holding back too many doses, according to two individuals with direct knowledge of the conversation who spoke on the condition of anonymity because they were not authorized to discuss it.

Scott Gottlieb, a former Food and Drug Administration commissioner in the Trump administration and a board member for Pfizer, has also repeatedly said the administration is being needlessly conservative in withholding vaccine. He has said that Pfizer has not had manufacturing problems and that Operation Warp Speed can be confident a second dose will be available when needed.

“This is a crisis,” Gottlieb said in discussing the pandemic on CBS’s “Face the Nation” on Dec. 6. “We need to get as many vaccines in arms as possible, in my view, and that means pushing out all the available supply, or most of it. You might want to hold a little bit in reserve, but not much.”

This view contrasts with those of many, but not all, of President Trump’s senior health officials, who maintain that reserves are essential while the manufacturing is relatively new. Otherwise, they have warned, some people would risk having that second dose delayed, or vaccines intended as initial doses might need to be diverted to be used as second doses for those who have received their initial shots.

In response to Biden’s plan, Operation Warp Speed spokesman Michael Pratt said in a statement, “If President-Elect Biden is calling for the distribution of vaccines knowing that there would not be a second dose available, that decision is without science or data and is contrary to the . . . approved label” from the FDA.

The FDA recently warned against extending the length of time between vaccine doses, cutting doses in half or using a single dose for a vaccine requiring two doses. Biden is not proposing any of those things. He is assuming that the companies will be able to produce second doses on time and planning for the federal government, if necessary, to take steps to ensure that.

State officials said they had not been consulted about Biden’s plans.

Cara Christ, Arizona’s top public health official, said whether to withhold second doses was not among the topics in a recent questionnaire sent to state officials by the transition team. She said she favored the change, telling reporters Friday that it “would allow us to expand our distribution greatly.”

Christ said that the change would require her department to be more forward-looking in case supplies remain short but added that she expects manufacturing to expand.

Jennifer Dillaha, state epidemiologist in Arkansas, said releasing nearly all available doses and not keeping some in reserve would require the state to shift its plans. She said she could not be more specific, however, until she knows more details of Biden’s plan. She added that the issue did not come up on a recent call with Biden advisers arranged by the National Governors Association.

Pfizer did not comment directly on Biden’s intentions but issued a statement saying the company “is confident in our ability to deliver 200 million doses” to the federal government by July 31, under a recently expanded agreement. “We are committed to collaborating with the Biden administration on common-sense solutions to the challenges in vaccine distribution,” the statement said.

Meanwhile, in Florida, authorities are investigating the death of a doctor 16 days after he received the Pfizer-BioNTech vaccine, but public health authorities have not established any link. They noted that unrelated deaths are inevitable after vaccine administration, given that millions are getting the shots.

The widow of Gregory Michael, an obstetrician-gynecologist in Miami Beach, suggested that his death Sunday after uncontrolled bleeding was a result of his vaccination about two weeks earlier. Darren Caprara, the director of operations at the Miami-Dade County Medical Examiner Department, said the office completed an autopsy Tuesday and sent samples to the CDC to try to determine whether his death was connected to the vaccine.

A Pfizer spokesman said the company is monitoring the death but does not believe it is related. The spokesman said the company is unaware of any similar cases.

Lena H. Sun and Brittany Shammas contributed to this report.