(Bloomberg) -- Five months after President Joe Biden declared the U.S. to be on the verge of defeating Covid-19, the virus threatens a winter resurgence across the country.

Biden on Thursday will sketch out his latest plan to quell the pandemic that’s dogged his presidency, a day after the first U.S. case of the omicron variant was identified in California. His latest measures include stricter testing requirements for air travelers arriving from abroad, extending a mask mandate and requiring private insurers to reimburse the cost of at-home tests.

Cases are already building in cold-weather states where Americans have begun to retreat indoors, where schools have been linked to outbreaks and where public health officials say they face widespread exhaustion with measures intended to prevent infections. Biden’s response is further complicated by omicron, which features mutations scientists believe could make it more transmissible and virulent.

“There’s a lot of pandemic fatigue. People are tired of thinking about Covid, they’re tired of taking precautions,” said Natasha Bagdasarian, Michigan’s chief medical executive. “Having an even more transmissible variant potentially come on top of an existing surge is our worst-case scenario.”

The first confirmed U.S. case of the variant was detected in California, after a person who returned from South Africa Nov. 22 tested positive, the Centers for Disease Control and Prevention announced Wednesday.

The delta variant-driven surge that began around Biden’s speech five months ago, marking the U.S. Independence Day holiday by celebrating the country’s reopening, hit mostly warmer, southern states led by Republicans. But the latest outbreaks are occurring in northern areas that are more politically sensitive for the president, such as Michigan, Pennsylvania and New Hampshire. 

Michigan’s Democratic governor, Gretchen Whitmer, is up for re-election next year, as is New Hampshire Senator Jeanne Shaheen, also a Democrat. Democrats hope to pick up a Pennsylvania Senate seat following the retirement of Republican Pat Toomey.

New Strategy

Severe Covid-19 remains overwhelmingly most common among vaccine holdouts, state health officials say. Biden and his team have tried to leverage concern about omicron to encourage unvaccinated Americans to relent and get shots. 

“We are clearly seeing, in terms of deaths and hospitalizations, this is a surge of the unvaccinated,” Bagdasarian said.

Biden will lay out his new strategy Thursday afternoon. Other highlights include a pledge to deliver 200 million more vaccine doses abroad in the next 100 days, doubling the number of free tests sent to community sites, to 50 million, and considering changes to school safety guidance, including potentially allowing kids to stay in class after an exposure under certain conditions.

The plan was in preparation before omicron emerged. Vaccines, along with the looming arrival of antiviral pills, will help reduce serious disease and deaths, which some of Biden’s advisers believe to be better metrics than raw case numbers.  

Shots continue to be a partisan issue in the U.S., reflected in a Republican push across the country against vaccine and mask mandates. Some Republican lawmakers are now threatening a government shutdown to protest Biden’s vaccine requirements, which have encouraged millions of workers to get shots. 

Thanksgiving and Christmas gatherings fueled a huge spike in cases last year, and officials are bracing for another one this year.

“Concerningly for us, we have noted an upward trend in the hospitalized population and we anticipate Covid-related deaths are going to increase,” said Alison Beam, Pennsylvania’s Acting Secretary of Health. Cases are expected to rise too, with people heading indoors and more family travel and gathering, along with omicron’s potential spread. 

“We’ve known that the virus thrives in those environments so those indicators would all point to increasing case counts,” she said. The state continues to work with community partners to encourage people to get a shot. 

Michigan has administered about 128 doses of vaccines per 100 people, less than the U.S. average of 138 per 100, according to the Bloomberg Vaccine Tracker. Pennsylvania has given 143 shots per 100. 

States with even lower vaccine coverage are watching Michigan warily.

“They’re the most recent canary in the mine. And for them, they’re better vaccinated than we are, and they’re struggling right now. So it’s a concern for sure,” said Clay Marsh, West Virginia’s Covid czar, who also leads the academic health sciences center at West Virginia University. 

As of this week, the state had about 500 Covid patients in hospitals, including 182 in intensive care -- not far from highs of last winter and well above levels of last Thanksgiving. West Virginia has given only about 94 shots per 100 people.

Case loads remain high in the state, which has the country’s lowest vaccination rate. “Our glass is much fuller this time looking at a potential next surge in the winter, so it makes us very nervous,” Marsh said.

Breakthrough Infections

While some states grapple with a pandemic of the unvaccinated, others face another challenge: waning vaccine protection. In New Mexico, about 25% to 30% of the current cases in the state are breakthrough infections, said David Scrase, a physician who serves as the state’s Health and Human Services secretary.

The state had strong vaccination totals early and now is among those seeing a surge, making it a test case for how quickly protection fades. “We kind of think we’re the tip of the spear,” he said in an interview.

New Mexico’s governor, Michelle Lujan Grisham, has declared the entire state high-risk as a way to make the entire population eligible for boosters sooner. While some state health officials report apathy among the public, New Mexico is seeing the opposite. “People tuned out in June, but I think they’re tuning back in,” Scrase said. 

The delta variant fueled a bump in vaccinations, as the unconvinced responded to an increased threat. Omicron may do the same, officials say. However, if it fizzles, Marsh fears that the unvaccinated will further tune out. “If you pull a fire alarm, there should be a fire,” he said.

The situation varies widely by state, complicating federal efforts. For instance, Michigan says its surge began in the fall and was driven by schools, where kids have low vaccination rates, before then spilling out into the community. 

“This school population was largely unvaccinated, they went back into these indoor settings, many of them without mask policies, and we saw a huge upswing in cases in 5- to 18-year-olds, and that then trickled into other age groups,” Bagdasarian said.

But in New Mexico, officials suspect cases in kids came from the community, not schools, Scrase said.

Biden and his top medical adviser, Anthony Fauci, have cautioned that it will take a few weeks to understand omicron’s threat. In the meantime, they’re focused on vaccinations.

“People should wind up getting vaccinated and boosted if they’re eligible for a boost,” Fauci said Wednesday. “I keep coming back to that because that’s really the solution to this problem.”

©2021 Bloomberg L.P.