(NewsNation Now) — For the first week of January, more than 2,000 schools were prepared to close for at least one day due to COVID-19 concerns, according to Burbio, a company that tracks school data.

There are 21 states with at least one school district closed or transitioning to remote learning this week.

Some schools might be closed for a day, others for the entire week as school districts nationwide are adjusting as students return to classrooms.

Back-to-school disruptions are the heaviest in the Northeast and Midwest, which have been hit hard by the omicron variant of COVID-19.

A lot of the largest school districts in the nation are choosing to rapid test students as they head back, including Chicago and Washington, D.C.

Los Angeles schools are not requiring a negative test to return, but they will be testing random groups of students throughout the week to determine how many cases there are in the school population.

Watch the full Smart Board report in the video player at the top of the page.