Biden plans to release nearly all available doses in an attempt to speed vaccinations.

President-elect Joseph R. Biden Jr. plans to release nearly all available coronavirus vaccine doses “to ensure the Americans who need it most get it as soon as possible,” the Biden transition team said Friday, a move that represents a sharp break from the Trump administration’s practice of holding back some of the vaccine.

“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,” T.J. Ducklo, a spokesman for the transition team, said.

“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. He will share additional details next week on how his Administration will begin releasing available doses when he assumes office on January 20th.”

Because both of the vaccines that have emergency approval require two doses, the Trump administration has been holding back roughly half of its supply to ensure those already vaccinated receive the booster dose. But the vaccine rollout has been troubled from the start.

As of Thursday, the Trump administration had shipped more than 21 million vaccine doses, and millions more were already in the federal government’s hands. Yet only 5.9 million people had received them. State and local public health officials, already overwhelmed with rising infections, have been struggling to administer the vaccine to hospital workers and at-risk older Americans while most people remain in the dark about when they might be protected.

Releasing the vast majority of the vaccine doses raises the risk that second doses would not be administered on time. Officials from the Food and Drug Administration — experts whose advice Mr. Biden has pledged to follow — have spoken out strongly against changing the dosing schedule, calling such a move “premature and not rooted solidly in the available evidence.” But a transition official, speaking anonymously to provide insight into the president-elect’s thinking, said he would use the Defense Production Act, if needed, to ensure that enough doses are available.