OKLAHOMA CITY (AP) — School districts across Oklahoma are shutting down or switching to virtual learning as a result of a surging number of coronavirus cases.

Oklahoma City and Putnam City public schools both announced Wednesday plans to shift to virtual learning through the end of the week, citing staffing shortages as a result of a spike in COVID-19 cases.

"Even after working to reassign staff at all levels across the district, we have determined that we can no longer adequately sustain a safe and meaningful learning environment for our students," OKCPS Superintendent Sean McDaniel wrote in a letter to parents. "This is a manpower issue, and we are simply out of options."

StateImpact Oklahoma, which is tracking school closures, reports more than 140 districts with schools either closing or switching to distance learning.

According to data from Johns Hopkins University, the seven-day rolling average of daily new cases in Oklahoma has risen over the past two weeks from 1,462 new cases per day on Dec. 27 to nearly 7,000 new cases per day on Monday. The seven-day average of daily deaths in the state has nearly doubled during the same time period, from 11.71 deaths per day on Dec. 27 to 22 deaths per day on Monday.

The highly contagious omicron variant has become the dominant strain of the coronavirus in Oklahoma, leading to increased cases and hospitalizations. It also more easily infects those who have been vaccinated or had previously been infected by prior versions of the virus. However, early studies show omicron is less likely to cause severe illness than the previous delta variant, and vaccination and a booster still offer strong protection from serious illness, hospitalization and death.