The decision to release the vast majority of vaccine doses set off a sharp debate among public health experts. The two vaccines that have received emergency approval each require two doses, and the Trump administration has so far been holding back about half of its supply to ensure that booster doses will be available for those already inoculated.

The announcement by the incoming Biden administration sets the clearest benchmark yet for front-loading shots, then distributing them as they become available. Officials at Operation Warp Speed, the Trump administration’s vaccine program, had noted that doses would stop being sequestered after the first few weeks of rollout. Both the health secretary, Alex M. Azar II, and Warp Speed officials were critical of the president-elect’s decision on Friday.

The Food and Drug Administration — whose advice Mr. Biden has pledged to follow — has spoken out strongly against changing the dosing schedule, as some other countries have opted to do, calling such a move “premature and not rooted solidly in the available evidence.” Some public health experts fear that second doses would be delayed by the decision.