The U.S. is undergoing a continuing shift to virtual learning as many states reverse reopenings due to another spike in COVID-19 cases.

As of Monday, according to data from Burbio, a community events data service that tracks school openings, 49% of K-12 students are attending school virtually, which is up from 43.5% last week, and 36.9% two weeks ago.

Meanwhile, 33.5% of K-12 students are attending school in person and 17.5% are attending a hybrid school program, with a mix of in-person and virtual instruction.

View Burbio’s K-12 School Opening Tracker

The increase in virtual instruction is spurred by post-Thanksgiving closures in the Midwestern and Northeastern regions, some until January and many for shorter periods, according to the service’s data.

Districts that are closing for only a brief period and offering virtual learning include those in Kansas, such as Topeka Public Schools, as well as in Iowa (Davenport Community Schools and Iowa City Community School District). Many individual schools within districts also recently shifted to virtual learning, Burbio’s data finds.

For districts in many parts of the country, instruction over the next few months will hinge on a balance of health regulations and instructional logistics.

In Pennsylvania, the state departments of health and education issued a joint letter outlining certification criteria for districts where there is "substantial" spread: currently comprising 59 of the 67 counties in the state. In Louisiana, the Associated Press reports that school administrators appealed to state health officials to loosen quarantine rules. In Colorado, Chalkbeat reports a letter from the Colorado Association of School Executives asking the governor to either support their closure decisions or loosen quarantine rules to allow them more flexibility.

In New York, Gov. Andrew Cuomo, realizing that many districts do not have the testing resources to stay open, announced plans to reallocate testing resources to schools to at least keep K-8 schools open through the winter months.

On Sunday, after recently closing schools to in-person learning, (the city had initially reopened some schools in late September), the New York City Department of Education announced that elementary school students will return to classrooms on Dec. 7 and attend in-person every weekday; this is subject to capacity issues in certain schools. High school and middle school students will remain virtual for now. This is a shift from the previous systemwide hybrid plan.

This plan has potential implications beyond New York City, Burbio states. It has been widely reported that elementary school students are less susceptible to COVID-19 than adolescents and can be more easily organized into "cohorts" than older students. In addition, younger students struggle with virtual learning, and by dispensing with the hybrid option, which creates logistical challenges in districts of all sizes, New York City is streamlining the in-person experience, offering a roadmap for other large urban districts. This could also preview how suburban and smaller city districts currently offering systemwide hybrid schooling might prioritize adding in-person learning at the elementary school level in 2021, according to Burbio.

With the announced return of a portion of New York City students, and some districts in the Northeast and Midwest planning to return to in-person school as soon as this month, the virtual-only figure may have just peaked, according to Burbio. However, an increase in closures in the Sun Belt, where schools have generally stayed open during the most recent increase in cases, would change that.

Additionally, it is worth noting, according to Burbio, that to date over 30% of K-12 students in the U.S. have not received any in-person instruction this academic year.