President Biden announced an array of measures Thursday to protect Americans from a potential winter surge of coronavirus infections, as five states confirmed cases linked to the omicron variant and international researchers shared data indicating that the still-mysterious variant may be able to reinfect people who had prior infections.

“We’re going to fight this variant with science and speed, not chaos and confusion,” Biden said in a speech at the National Institutes of Health, appealing to Americans to put aside partisan differences and continue to get vaccinated, wear masks and take other precautions. “This is a moment we can put the divisiveness behind us, I hope.”

The president’s plan includes campaigns to increase vaccinations and booster shots, more stringent testing for international travelers and plans to make rapid at-home coronavirus testing free for more people. While some of the measures are new — notably a plan to launch “family mobile vaccination clinics,” where all eligible members of a family could simultaneously get shots and boosters — others build on existing tactics, such as rallying businesses to impose vaccination-or-testing mandates for employees.

Public health experts praised aspects of Biden’s plan but called for further investments in testing, screening and combating misinformation about the vaccines. They also said Biden’s vow that the nation will ward off omicron after it “beat back” the delta variant doesn’t reflect a reality where the virus continues to circulate at high levels, with more than 140,000 coronavirus-linked deaths in the United States since the start of September.

It’s the “most aggressive pandemic plan yet for the United States, but still falls short of all that’s needed now,” said Eric Topol, director of the Scripps Research Translational Institute.

Biden’s package of coronavirus strategies comes as officials confirmed omicron-linked infections in California, Minnesota, Colorado, New York and Hawaii, and as South African researchers reported that the new variant appeared to be linked to increased coronavirus re-infections, although the new cases were mild. Scientists caution that it will take days, if not weeks, to fully understand whether the new variant can evade current vaccines and treatments, or cause more severe symptoms in infected people.

On Dec. 1, top infectious-disease expert Anthony S. Fauci said the first case of the omicron coronavirus variant had been detected in California. (The Washington Post)

In his remarks, Biden stressed that the vaccines remain the best protection against existing and new variants and that all adults should get a booster shot as soon as they are eligible, given that immunity appears to wane over time — a position increasingly echoed by public health experts.

“Starting today, we’re making it easier than ever to get a booster shot,” the president said, touting a plan for pharmacies to send text messages and emails to remind Americans when they are due for the additional shots. The federal health department also will launch new booster-shot ad campaigns and partnerships with organizations like AARP, the advocacy group for older Americans.

In addition, the plan calls for Medicaid, the safety-net health insurance program, to reimburse participating health-care providers for “COVID-19 counseling visits,” in which health workers answer families’ questions about vaccines and stress the importance of getting children immunized.

But it was unclear whether such plans would spur significant movement on vaccinations at a time when new shots have slowed and attitudes appear to have hardened. Fifty-eight percent of Americans were considered “fully vaccinated” against the coronavirus as of Nov. 1 — a rate that climbed to only 59.4 percent as of Dec. 1, according to The Washington Post’s vaccination tracker.

There is also emerging evidence of a widening partisan gap among Americans choosing to get a booster shot. The Kaiser Family Foundation on Thursday reported that 32 percent of vaccinated Democrats have received a booster shot, compared with 21 percent of independents and 18 percent of Republicans. Meanwhile, 31 percent of fully vaccinated Republicans said they definitely or probably would not get a booster shot.

“We saw partisanship play out as the biggest predictor of whether people would get a first shot,” said Liz Hamel, a Kaiser Family Foundation vice president. “Now we’re seeing that even among the fully vaccinated, Republicans are less eager to get boosters.”

But the threat of omicron could change minds, Hamel added. Federal officials on Thursday announced that 2.18 million total doses had been administered to Americans in the past 24 hours — the highest total in more than six months, White House Covid-19 Data Director Cyrus Shahpar wrote on Twitter. The tally includes 678,000 first doses administered to previously unvaccinated Americans, and more than 1 million boosters.

Meanwhile, Biden touted a plan to make rapid at-home tests more available by requiring private insurance companies to reimburse consumers for the cost of the tests, beginning in January, while community health centers and some rural clinics offer them free. “Private insurers already cover the expensive PCR test that you get at a doctor’s office, and now they will cover at-home tests as well,” the president said, although the plan will not apply retroactively to already purchased tests.

Some public health experts said they had questions about how the model — which calls for the departments of Health and Human Services, Labor and Treasury to issue federal guidance by Jan. 15 — would be implemented.

Nirav D. Shah, president of the Association of State and Territorial Health Officials and director of Maine’s Center for Disease Control and Prevention, said state officials are hoping the reimbursement would be approved in real time when someone bought the test — in the same way such claims are processed and approved when people get flu shots and prescription medications.

“Lumping in the covid test under that model would greatly expand access,” he said during a news conference Thursday.

Others argued it would be better for the government to buy the tests and distribute them widely at no charge.

Using private health insurance is “a sucker strategy,” said Tinglong Dai, professor of operations management and business analytics at the Johns Hopkins University Carey Business School. “You have to buy this test and then get reimbursed; it’s a lot of hassle.”

In addition, he said, insurance companies eventually raise premiums to recoup their costs. “Nothing is really free,” he said.

Coronavirus variants like omicron, delta and mu are an expected part of the virus's life cycle, but vaccines can prevent more infectious variants from forming. (John Farrell, Hadley Green/The Washington Post)

Public health experts have spent months clamoring for more access to rapid coronavirus testing, warning that the lack of real-time data on infections has had disastrous consequences for containing the virus’s spread.

“Free and highly available rapid tests would be a game changer,” said Charity Dean, a former California health official and the CEO of the Public Health Company. “If we had rapid tests at every door for every school, every movie theater, any person can go and get them — just like they can in many other countries — it would enable people to have personal responsibility and know when they’re infectious.”

Shah, head of Maine’s CDC, stressed the continued difficulty that states have had in obtaining rapid at-home tests from manufacturers, as well as securing funding to pay for them. State health departments buy tests in bulk for schools, nursing homes, prisons and other places experiencing local outbreaks.

In Maine, officials have ordered tens of thousands of Abbott’s BinaxNOW rapid at-home antigen tests for delivery, but Abbott has not delivered in a timely fashion, Shah said. While there are other authorized rapid tests on the market, state officials need to send the same test to institutions because “that’s what they know how to use,” he said.

Biden also announced that inbound international travelers must be tested for the coronavirus within one day of global departure, regardless of nationality or vaccination status. The policy, which takes effect Dec. 6, toughens protocols for vaccinated travelers, who had been able to get tested as long as three days before departure. The move, which federal officials had weighed earlier this week, comes after the White House imposed travel restrictions on eight nations in southern Africa following warnings from scientists about the emergence of the omicron variant.

Celine Gounder, an epidemiologist and infectious-disease specialist who advised Biden’s transition team on the coronavirus response, said she was unhappy that the White House prioritized restrictions and testing for international travelers while overlooking domestic flights.

“When you think about Texas, it’s the size of France — and it operates as its own country in many respects,” Gounder said, calling for a renewed focus on how state policies contribute to the virus’s spread. “If you’re really trying to prevent spread of dangerous variants, you should be providing similar standards across the board.”

Asked about additional restrictions on domestic and international flights, White House press secretary Jen Psaki said Thursday that “nothing is off the table” when it comes to controlling the virus’s spread. Psaki said the administration is considering what is “most implementable” but noted that “our most important factor is what is going to be most effective.”

Biden also extended requirements that travelers wear masks on airplanes, public transportation and trains, as well as in transportation hubs such as airports and bus stations. The measures, which were set to expire in January, will run through at least March 18, and the minimum fine for noncompliance will be doubled to $500. But the administration’s plan does not include new masking or vaccination mandates — a move that White House officials characterized as unnecessary and that public health experts said would be difficult to implement.

“I feel like they’ve kind of maxed out what they can do with mandates, from a political perspective,” Gounder said.

Some experts said renewed shutdowns in the wake of omicron’s emergence probably would be unnecessary.

“The reason why we had to do broad shutdowns and broad stay-at-home orders in March 2020 was because we were flying blind” and lacked information on the virus or how to fight it, Dean said. “Today … we can use the tools at our disposal to execute containment and mitigation with surgical precision.”

Biden’s plan arrives as White House officials are in constant communication with their counterparts overseas and vaccine manufacturers about the potential impact of the omicron variant.

Biden and his aides have long said his political fortunes are tied to the pandemic response. After a difficult summer highlighted by climbing covid cases, a chaotic withdrawal from Afghanistan and supply chain disruptions, White House officials were optimistic about shifting the focus to the president’s economic agenda as the ravages of the delta variant subsided. But the emergence of a new and potentially more dangerous variant has complicated the president’s messaging efforts.

“I expect this not to be the new normal,” Biden said Monday when asked whether the country should get used to the idea of new variants and occasional rounds of travel restrictions.

Laurie McGinley contributed to this report.