The tone of the hour-long briefing on Wednesday was in line with President Joe Biden's promise to be straight with the nation about the state of the outbreak that has already claimed more than 425,000 US lives.

It marked a sharp contrast to what had become the Trump show in the past administration, when public health officials were repeatedly undermined by a president who shared his unproven ideas without hesitation.

The deaths projection wasn't much different from what Biden himself has said, but nonetheless served as a stark reminder of the brutal road ahead.

"I know this is not news we all want to hear, but this is something we must say so we are all aware," said Dr. Rochelle Walensky, the new director of the Centers for Disease Control and Prevention.

"If we are united in action we can turn things around."

The new briefings, set for three times a week, are part of Biden's attempt to rebuild trust and mobilise Americans to follow health guidance on the coronavirus and to break down public resistance to the vaccine.

Wednesday's briefing was conducted virtually. One by one, the officials laid out administration efforts to contain the virus, speed vaccinations and bring Americans along with the effort..

"The White House respects and will follow the science, and the scientists will speak independently," promised Andy Slavitt, a senior administration adviser on the pandemic.

Jeff Zients, the White House coronavirus coordinator, said the Biden administration was examining additional ways of speeding vaccine production, a day after the president announced the US plans to provide states with enough doses for 300 million Americans by the end of summer.

But actually injecting those shots is another matter.

"Most states are getting better at putting needles in arms," Zients said. He called on Congress to swiftly pass Biden's "American Rescue Plan."

The $US1.9 trillion ($A2.5 trillion bill), which has given lawmakers in both parties sticker shock, includes $US400 billion ($A517 billion) for measures aimed at controlling the virus, including dramatically increasing the pace of vaccination and ensuring more widespread testing.

Dr. Anthony Fauci, the nation's top infectious disease expert, said there was reason to be concerned about the impact of some coronavirus mutations on vaccines, but he also said scientists have plenty of options for adjustments to maintain effectiveness.

Trump had claimed centre stage and muddled the message of the nation's top public health experts in the critical early days of the virus and eventually largely muzzled them as the pandemic's toll grew steeper.

The stakes for Biden, whose presidency hinges at the start on his handling of the pandemic and the largest vaccination campaign in global history, could hardly be higher.

He is pushing a weary populace to recommit to social distancing measures and mask wearing, pointing to scientific models that suggest the practices could save 50,000 lives over coming months.

Australian Associated Press