• Walgreens said the "unprecedented increase in demand" for rapid at-home Covid tests started after Thanksgiving and has continued through the week of Christmas.
• CVS said at-home Covid may be temporarily out of stock online.
• Abbott Laboratories, maker of the popular at-home Covid test BinaxNOW, is shipping its test as quickly as the company can produce them, spokesperson John Koval told CNBC.

Walgreens and CVS Health on Tuesday limited how many at-home Covid tests customers can purchase as demand for tests surges ahead of the holidays and as the omicron variant spreads throughout the U.S.

Walgreens has imposed a limit of four at-home tests per purchase, while CVS is allowing six tests per purchase. The purchase limits apply in-store as well as online.

"Due to the incredible demand for at-home rapid testing, we put in effect a four item purchase limit on at-home COVID-19 testing products in our stores and digital properties in an effort to help improve inventory while we continue to work diligently with our supplier partners to best meet customer demands," Walgreens spokesperson Emily Hartwig-Mekstan told CNBC.

Hartwig-Mekstan said that the "unprecedented increase in demand" for rapid at-home Covid tests started after Thanksgiving and has continued through the week of Christmas. CVS spokesperson Michael DeAngelis said at-home tests may be temporarily out of stock online due to the surge in demand.

The Biden administration announced a plan on Tuesday to distribute 500 million at-home Covid tests that Americans can order for free through a website the government is setting up. However, delivery of the free tests won't start until January, after the holiday travel season is largely over.

Abbott Laboratories, maker of the popular at-home Covid test BinaxNOW, is shipping its test as quickly as the company can produce them, spokesperson John Koval told CNBC.

The New York Times reported in August that workers at an Abbott factory in Maine were told to throw out millions of kit components as sales dropped due to a decline in demand driven by falling Covid cases throughout June and July.

Koval said Abbott didn't destroy any finished BinaxNOW testing supplies, saying test components have been in short supply during the coronavirus pandemic. Abbott is now making 50 million tests a month with production expected to increase to 70 million in January, he said.

However, Americans need the tests now as they navigate crowded airports and travel on full planes ahead of the holidays. Many people have come to rely on the convenience and quick results of at-home tests to make sure they are not Covid positive before traveling or gathering with friends and family.

Outgoing New York City Mayor Bill de Blasio on Monday said his administration is working with the White House to alleviate shortages in the Big Apple. New York City is currently the epicenter of the rapidly spreading omicron epidemic in the U.S., with new infections skyrocketing across the five boroughs.

"We're finding the supplies are becoming a challenge because all over the country testing is going up suddenly and we're seeing a supply problem that needs to be addressed," De Blasio said Monday.

Omicron is more transmissible than past strains of the virus. A real-world study out of the United Kingdom found that a booster of Pfizer and BioNTech's vaccine provides high levels of protection against symptomatic disease. The initial two-dose series still protects against severe illness, according to data from South Africa. However, the original vaccination series is only 33% effective at prevention infection, according to the data.

Correction: Abbott Laboratories makes the popular at-home Covid test BinaxNOW. An earlier version misstated the name of the product.