CVS and Walgreens, two of the biggest pharmacy chains in the United States, are temporarily closing some stores this weekend because of staff shortages complicated by the soaring number of people infected with the omicron variant.

Mike DeAngelis, a spokesperson for CVS, said the “vast majority” of stores were operating with normal hours this weekend. There are more than 9,900 CVS stores across the United States.

“A tiny fraction of stores are temporarily closed on one or both days of the weekend to help address acute staffing issues amidst both the omicron surge and the workforce shortage affecting nearly every industry and company,” DeAngelis said in an email.

Rebekah Pajak, a spokesperson for Walgreens, said closures were at a “small percentage” of the company’s more than 9,000 stores, and in most cases, the affected stores would be open at least one weekend day.

“When making the difficult decision to adjust store hours, we make every effort to minimize disruption for our customers,” Pajak said in an email. “We select days with the lowest prescription demand, ensure that there is a nearby pharmacy to meet any immediate prescription needs and provide patients as much advanced notice as possible through signage, automated phone calls and adjustments in refills.”

There has been a jump in coronavirus cases in most of the country in the past two weeks, although cases are starting to decline or level off in cities including New York and Cleveland, which had omicron-driven surges in recent weeks.

Worker shortages have been worsened by the omicron wave in industries including health care and air travel. Retail workers have also described how they have had to grapple with increased workloads and shifting guidelines because of the omicron surge.

This article originally appeared in The New York Times.