A surge in cases in the Upper Midwest has some Michigan schools keeping students at home ahead of Thanksgiving and the military sending medical teams to Minnesota to relieve hospital staffs overwhelmed by COVID-19 patients.

The worsening outlook in the Midwest comes as booster shots are being made available to everyone in a growing number of locations. Massachusetts and Utah became the latest to say anyone 18 or older can roll up a sleeve for a booster shots, and an advisory committee for the Centers for Disease Control and Prevention is meeting Friday to discuss expanding boosters.

Cold weather states are dominating the fresh wave of cases over the last seven days, including New Hampshire, North Dakota and Wisconsin, according to federal data. But the Southwest had trouble spots, too, with more than 90% of inpatient hospital beds occupied in Arizona.

In Detroit, where only 35% of eligible residents were fully vaccinated, the school district said it would switch to online learning on Fridays in December because of rising COVID-19 cases, a need to clean buildings and a timeout for “mental health relief.” One high school has changed to all online learning until Nov. 29.

At another high school, some students and teachers briefly walked out Wednesday, saying classes still were too large for a pandemic and the school needed a scrubbing.

Detroit health officer Denise Fair Razo said new cases have skyrocketed in the city in the last 14 days to 3,858, compared to 2,322 in the previous two-week period.

“We’re in Michigan so we’re not finding ourselves spending time outdoors in flip-flops and tank tops,” Fair Razo said Thursday. “We are indoors and we’re frankly becoming a little bit too relaxed. We’re no longer wearing our masks. We’re no longer washing our hands as frequently as we should. But we know these precautions.”

Fair Razo is urging people to get tested for COVID-19 before gathering at Thanksgiving, even if they’re vaccinated. She “absolutely” predicts a post-holiday spike.

Elsewhere in Michigan, some schools are taking next week off for the Thanksgiving holiday instead of just three days.

“This school year has presented some major stressors that are noticed and recognized,” Superintendent Greg Helmer told parents, citing staff shortages and student absences in Ravenna.

In Minnesota, the U.S. Defense Department will send two 22-member medical teams to Hennepin County Medical Center and St. Cloud Hospital next week to immediately treat patients and assist weary health care workers.

“I need Minnesotans to recognize, as we’ve been saying, this is a dangerous time,” Gov. Tim Walz said in pushing vaccinations.

New Hampshire reported 327 people with COVID-19 in hospitals, passing its previous pandemic high from last Dec. 31. Neighboring Maine also hit a high mark for COVID-19 hospitalizations this week.

Vermont Gov. Phil Scott is calling legislators into a special session next week to pass a bill giving local governments the power to adopt temporary mask mandates. He has been opposed to a statewide mask order even as Vermont’s new daily cases approach numbers not seen since the earliest days of the pandemic.

In Florida, Republican Gov. Ron DeSantis signed a law that prevents businesses from ordering workers to be vaccinated unless they also allow them to opt out for a variety of reasons, including regular testing. Schools and local governments are barred from making vaccination mandates, and parents can sue schools over masks.

Florida lately has one of the lowest rates of new cases in the country. DeSantis has become one of the nation’s most prominent Republicans through his opposition to lockdowns and other virus rules.

The U.S. is now averaging nearly 87,000 new coronavirus cases per day, up from 72,000 two weeks ago, and hospitalizations are starting to increase again after steadily falling since the peak of the summer delta variant surge. The country is still averaging more than 1,100 deaths a day, and the number of Americans to die from COVID-19 now stands at 768,000.

About 59% of the U.S. population is fully vaccinated, or about 195 million Americans. The government and health officials are urging more people to get vaccinated, especially the 60 million people who have yet to receive a first dose.