Mr. Biden has continued to offer federal support to states grappling with the Omicron variant’s impact, deploying the Federal Emergency and Management Agency to assist hospital systems in hard-hit areas. But he has deferred to state and local officials on setting pandemic policies on masks and schools. His administration also has put out a series of vaccination requirements for workers, some of which were delayed by court battles. Mr. Biden has continued to promote those requirements but focused more recently on the dangers for unvaccinated people.

Top aides to Mr. Biden argue the pandemic is in a different phase than a year ago, with more than 200 million people in the U.S. now fully vaccinated and nearly 72 million booster shots administered. But they are also urging people to stay vigilant and get vaccinated.

Mr. Biden’s top health advisers have also said the virus is unlikely to be eradicated anytime soon and placed a greater emphasis on preventing further disruptions to the economy and society. The White House stressed multiple times this week that K-12 students should remain in classrooms.

“Parents want schools open and experts are clear that in-person learning is best for kids’ physical and mental health and further education,” White House Covid-19 coordinator Jeff Zients said. “And the president couldn’t be clearer: Schools in this country should remain open.”

The CDC last week overhauled its guidelines for people who test positive for Covid-19, cutting the number of days that they recommend people isolate after being infected to five days from 10—if they haven’t had a fever in 24 hours without using medication and their other symptoms have improved.

The guidance change received criticism from some public health experts, who said that ending isolation around day five without a negative Covid-19 test could further the coronavirus’s spread, since some people could still be infectious at that point.

The agency updated its recommendations Tuesday, saying that an infected person who wants to get tested should use an antigen test toward the end of their five-day isolation period. If the person tests positive, they should continue to isolate until day 10, and if they test negative, they can end isolation but should continue wearing a mask around others for five more days. The agency stopped short of saying that people should get a rapid test before going back to work or resuming social activities.

The administration has stepped up its communications around the pandemic through weekly briefings between Mr. Biden and his health team, during which the president often addresses the public, and by increasing the number of briefings held by the White House Covid-19 response team. Anthony Fauci, Mr. Biden’s chief medical adviser, remains a fixture on national television and often uses public appearances to highlight how the pandemic has evolved.

Dr. Fauci said Wednesday that preliminary data showed the Omicron variant is less severe than previous strains. But he said the sheer volume of cases would likely overwhelm hospital systems once more.

“The big caveat is we should not be complacent,” Dr. Fauci said. “So don’t take this as a signal that we can pull back from the recommendations.”