WASHINGTON >> As many as 90,000 Americans are projected to die from the coronavirus in the next four weeks, the Biden administration warned in its first science briefing on the COVID-19 pandemic, as experts outlined efforts to improve the delivery and injection of COVID-19 vaccines.

The hourlong briefing today by the team charged by President Joe Biden with ending the pandemic, was meant to deliver on his promise of “leveling” with the American people about the state of the outbreak that has already claimed more than 425,000 U.S. lives. It marked a sharp contrast from what had become the Trump show, in the last administration, when public health officials were repeatedly undermined by a president who shared his unproven ideas without hesitation.

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

Today’s briefing was conducted virtually, rather than in person at the White House, to allow for questions from health journalists and to maintain a set timing no matter the situation in the West Wing. But it was not without technical glitches.

It featured Jeff Zients, the Biden administration’s coordinator for pandemic response; his deputy, Andy Slavitt; Dr. Anthony Fauci, the nation’s top infectious disease expert; Dr. Marcella Nunez-Smith, the chair of Biden’s COVID-19 equality task force, and Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention.

“The White House respects and will follow the science, and the scientists will speak independently,” said Slavitt.

Zients, who previously ran the Obama administration’s efforts to salvage the rollout of HealthCare.gov, used to sign up for Affordable Care Act insurance exchanges, repeated that the federal government no longer has a stockpile of vaccines to distribute. He added that the Biden administration was examining additional ways of speeding vaccine production, a day after the president announced the U.S. plans to have delivered enough doses for 300 million Americans by the end of summer.

But injecting them in arms is a different matter.

“Most states are getting better at putting needles in arms,” Zients said, called on Congress to swiftly act to pass Biden’s “American Rescue Plan.” The $1.9 trillion bill includes $400 billion for measures specifically aimed at controlling the virus, including dramatically increasing the pace of vaccinations and building out an infrastructure for widespread testing.

Zients added that the federal Department of Health and Human Services acted today to make more professionals available to administer vaccinations. The government will authorize nurses and doctors who have retired to administer vaccines, and professionals licensed in one state will also be able to give shots in other states. Such measures are fairly standard in health emergencies.

Fauci told reporters there was reason to be concerned about the impact of some coronavirus mutations on vaccines, but that scientists have plenty of options for adjustments to maintain the effectiveness of vaccines and treatments.

Fauci said there was particular concern about the so-called South African variant, because lab tests have shown that it can diminish the protective power of the vaccines approved to date. He stressed that the level of protection provided was still well within what he called the “cushion” of vaccine effectiveness, but added that the government was working with pharmaceutical companies on potential “booster” shots for the new variants.

Walensky, the new head of the CDC, said her agency’s latest forecast indicates the U.S. will reach between 479,000 and 514,000 deaths by Feb. 20. More than 425,000 Americans have already died in the pandemic.

The new thrice-a-week briefings, beginning just a week into Biden’s tenure, are meant as an explicit rejection of Donald Trump’s approach to the coronavirus outbreak.

“We’re bringing back the pros to talk about COVID in an unvarnished way,” Biden told reporters Tuesday. “Any questions you have, that’s how we’ll handle them because we’re letting science speak again.”

Trump claimed center 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 mortal toll grew steeper.

The new briefings are part of Biden’s attempt to rebuild public confidence in institutions, particularly the federal government, with a commitment to share the bad news with the good.

“I’ll always level with you about the state of affairs,” he said Tuesday, repeating a central pledge of his inaugural address.

It’s a message that helped carry Biden to the White House. As a candidate he warned that the nation faced a surge of coronavirus cases in what would be a “dark winter”; Trump, for his part, falsely claimed the worst of the virus was over.

Dr. David Hamer, a professor of global health and medicine at Boston University’s School of Public Health, said having briefings from health officials that are “based on serious science” would go a long way toward improving public perceptions of the vaccine.

“There’s a certain amount of vaccine hesitancy, and so educating people about the vaccine, how it works, how safe it is and how it can protect against the disease but also slow transmission is really important,” he said.

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

Biden 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 the coming months. He has insisted members of his administration model best behaviors for the country.

Those messages found few champions in the former administration, as Trump openly flouted science-based guidance from his own administration. Face coverings were sparse at his reelection rallies and social distancing nearly nonexistent.

In the weeks leading up to Biden’s inauguration, the U.S. set records in new cases and reported deaths almost by the day, as many states reimposed costly restrictions to slow the spread of the virus. Even so, Trump restricted media appearances by his top scientists and public health officials and continued to spread misinformation.

Asked by CNN last week if the lack of candor from the Trump administration about the virus had cost lives, Fauci replied, “You know, it very likely did.”

The Trump administration ended the practice of regular scientific briefings early in the pandemic, after Trump expressed anger over dire warnings about the virus by Dr. Nancy Messonnier, the CDC’s immunization and respiratory director who is leading the agency’s COVID-19 efforts.