By Sabrina Siddiqui and Stephanie Armour

WASHINGTON -- President-elect Joe Biden will seek to release nearly all available coronavirus vaccine doses to accelerate distribution, his transition team said Friday, in a shift from the Trump administration's policy of holding back stock for second doses.

"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," said TJ Ducklo, a spokesman for Mr. Biden's transition. "He supports releasing available doses immediately, and believes the government should stop holding back vaccine supply so we can get more shots in Americans' arms now."

Mr. Ducklo said Mr. Biden, who will be inaugurated on Jan. 20, will release additional details about his vaccine distribution plans next week. They include establishing federally run vaccination sites, as well as mobile units that can travel to rural and underserved areas, and the launch of a national public awareness campaign around vaccine safety and guidelines, said incoming White House press secretary Jen Psaki.

The announcement comes as the U.S. and many other countries are struggling to ramp up vaccination programs. The Trump administration had promised to vaccinate 20 million people by the end of 2020.

The administration has been holding back about half of the vaccination doses for second shots. The administration has distributed 21.4 million vaccination doses from Moderna Inc. and Pfizer Inc. with BioNTech SE, and 5.9 million people have received the first dose as of Jan. 7, according to the Centers for Disease Control and Prevention.

"Vaccines give us hope, but the rollout has been a travesty," Mr. Biden told reporters in Wilmington, Del., on Friday.

Some medical authorities, including the U.S. Food and Drug Administration, have said delaying the second dose of the vaccine is potentially detrimental to public health. A Biden transition official said the president-elect is confident that manufacturers can produce enough vaccines to deliver second doses in a timely manner, while adding Mr. Biden will use the Defense Production Act to boost supply.

The Biden team's decision won't change the timing interval between first and second doses, according to a person familiar with the administration's planning.

The release of more vaccination doses could further strain some states that have for months been calling for more funding from the Trump administration and Congress to help them staff up and handle administration of the shots.

Congress in December approved a vaccine relief package that includes about $8 billion for states. But some states may have to hire and train staff, which some public health officials have said can take five to six weeks.

"Public health has been scaled up to deal with it, but vaccine allocation has not gone up," said Claire Hannan, executive director of the Association of Immunization Managers, which works with states and territories on immunization. "We keep thinking it's going to ramp up and it isn't."

Mr. Biden said Friday he will seek a significantly larger coronavirus relief package upon taking office, which would include more funding for local and state officials as they grapple with the pandemic and vaccine distribution. "The price tag will be high," Mr. Biden said.

A Pfizer spokeswoman said the company is confident in its ability to deliver 200 million doses of the vaccine to the U.S. government by the end of July.

"We are committed to collaborating with the Biden administration on common-sense solutions to the challenges in vaccine distribution so that as many Americans as possible have access to our vaccine as quickly as possible," the spokeswoman said.

Mr. Biden will get his second dose of the vaccine next week, his incoming White House press secretary Ms. Psaki said Friday. He received his first dose last month before cameras in a bid to instill public confidence in the vaccine. Ms. Psaki said the vaccine was also being administered to other top officials who will be close to the president-elect in the administration.

News of the Biden administration's release plan was first reported by CNN.

The release plan follows a letter from a group of Democratic governors to Health and Human Services Secretary Alex Azar and Operation Warp Speed Chief Operating Officer Gen. Gustave Perna asking the federal government to immediately begin distributing reserved doses.

Mr. Biden has promised a more robust response to steering the nation out of the coronavirus pandemic, which has infected more than 21 million people across the U.S. and claimed more than 360,000 lives.

The decision could help increase the number of people who receive the vaccine. But it also raises the risk of not having reserves to provide booster shots and could strain some states that lack the staffing or infrastructure to meet potential demand.

Some state public health officials said they haven't yet received information from Mr. Biden's transition team on changes to the vaccine rollout that may be planned, which they say they need to anticipate any hiring or workflow changes.

U.S. Department of Health and Human Services leaders who have been overseeing the coronavirus response team are preparing to leave, and some staff who handle communication and coordination have been told they will be replaced after they offered to stay in their roles to help during the transition. Concerns are mounting that the vaccine rollout could be further disrupted by the changeover, according to two people familiar with the planning.

"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 FDA's approved label," said Michael Pratt, a spokesman for Operation Warp Speed.

"If President-elect Biden is suggesting that the maximum number of doses should be made available, consistent with ensuring that a second dose of vaccine will be there when the patient shows up, then that is already happening," he added. "Second-dose management was always about ensuring supply-chain availability."

The vaccine rollout has been sluggish. Dr. Anthony Fauci, the U.S. government's top infectious-diseases official, said this week that the U.S. will soon be able to give one million vaccinations a day. But even that stepped-up pace would put the country on track to fully immunize 80% of the population by June of 2022.

"We really should be at at least three million a day," said Ashish Jha, dean of the Brown University School of Public Health, who on Friday praised the decision to release more of the second doses.

Pressure has been growing from public-health officials and Democratic state leaders to release the second doses, and the urgency has risen because a new, more transmissible strain of the virus has been found in the U.S. California Democratic Gov. Gavin Newsom and New York Gov. Andrew Cuomo, also a Democrat, this week pressed HHS to release second doses.

The White House coronavirus task force this week had discussed possible changes to the vaccine rollout, including whether more vaccines should be sent to states that are making more rapid progress on getting shots administered, according to a person familiar with the discussions.

They also discussed possibly allowing second shots to be given at five or seven weeks after the first, instead of at three or four weeks, the person said. The decision to hold back second doses wasn't made by the task force, the person said.

--Jared Hopkins and Tarini Parti contributed to this article.

Write to Sabrina Siddiqui at Sabrina.Siddiqui@wsj.com and Stephanie Armour at stephanie.armour@wsj.com

Corrections & Amplifications

This item was corrected at 6:37 p.m. ET. An earlier version misstated Claire Hannan's surname as Hannon.

(END) Dow Jones Newswires

01-08-21 1659ET