The slow pace is frustrating health officials and a desperate public alike, with about a third of the first supplies shipped to states over the past few weeks used as of Tuesday morning.
Anytime you start a big programme, there's always glitches. I think the glitches have been worked out, the nation's top infectious disease expert told AP.
Vaccinations only began on Dec 14 and already had begun speeding up, reaching roughly half a million injections a day recently, he pointed out.
Now with the holidays over, once you get rolling and get some momentum, I think we can achieve one million a day or even more, Fauci said.
He called US President-elect Joe Biden's goal of 100 million vaccinations in 100 days a very realistic, important, achievable goal.
It's an optimistic prediction considering the logistical hurdles facing states and counties as they struggle to administer rationed vaccine supplies amid rising COVID-19 hospitalizations. Fauci pointed to California's swamped hospitals as well as exhausted personnel even before holiday travel.
The coronavirus has killed more than 356,000 Americans, and the next few weeks could bring another jump in infections nationally that could make matters even worse, he said.
The Trump administration had promised to provide states enough vaccine for 20 million people in December, and fell short even as states struggled with their role getting shots into people's arms, starting mostly with health care workers and nursing home residents.
According to the Centers for Disease Control and Prevention, roughly 4.8 million doses of more than 17 million delivered had been used by Tuesday morning likely an undercount due to delays in reporting but still far fewer than experts had hoped.