Some school systems around the U.S. extended their holiday break Monday or switched back to online instruction because of the explosion in COVID-19 cases, while others pressed ahead with in-person classes amid a seemingly growing sense that Americans will have to learn to co-exist with the virus.

Caught between pleas from teachers fearful of infection and parents who want their children in class, school districts in cities such as New York, Milwaukee, Chicago, Detroit and beyond found themselves in a difficult position midway through the academic year because of the super-contagious omicron variant.

New York City, home of the nation’s largest school system, reopened classrooms to roughly 1 million students with a stockpile of take-home COVID-19 test kits and plans to double the number of random tests done in schools.

“We are going to keep our schools open and ensure that our children are in a safe environment,” newly sworn-in Mayor Eric Adams said.

New Yorker Trisha White said that she feels the risk is the same for her 9-year-old son in or out of school and that being with classmates is far better for him than remote learning.

“He could get the virus outside of school,” she said as she dropped the boy off. “So what can you do? You know, I wouldn’t blame the school system. They’re trying their best.”

While the teachers union had asked the mayor to postpone in-person learning for a week, city officials have long said that mask requirements, testing and other safety measures mean that children are safe in school. The city also has a vaccination mandate for employees.

New cases of COVID-19 in the city shot up from a daily average of about 17,000 in the week before the holidays to nearly 37,000 last week.

Across the U.S., new COVID-19 cases have tripled in the past two weeks to over 400,000 a day, the highest level on record, amid a rush by many Americans to get tested.

The high infection rates and resulting worker shortages are putting a heavy burden on employers large and small. Thousands of airline flights have been canceled in recent days, and many businesses have shelved return-to-work plans.

Weekend garbage collection was delayed in New Orleans, and jury trials in several Colorado counties were suspended. Some libraries on New York’s Long Island and a ski resort in New Hampshire had to close. A restaurant owner in Atlanta has spent $700 on rapid test kits and resorted to testing workers in the parking lot to make sure he had enough help to staff a recent dinner shift.

Dawn Crawley, CEO of House Cleaning Heroes, a cleaning service based in Herndon, Virginia, said she had to cancel four of 20 cleaning jobs for Tuesday because four employees were sick — three with COVID-19.

“The fear is it will run through the team” as well as customers, she said.

Policymakers and health authorities have been mindful of the toll on the economy and the education system.

Public heath experts have said that eradicating the virus is unlikely and that the world will instead have to find a way to keep COVID-19 down to an acceptable level, the way it does with the flu.