The Centers for Disease Control and Prevention has added exceptions to its official guidelines for administering the Pfizer-BioNTech and Moderna vaccines in case of a supply holdup.

Although its official stance is that the two vaccines should not be used interchangeably, one can replace the other when the same vaccine is not available for a second dose, the agency now says. (The two vaccines are similarly formulated.) In addition, the delay between doses can be stretched up to six weeks if vaccination is not possible sooner. (The official dose interval recommendation is three weeks for Pfizer-BioNTech or one month for Moderna.)

The agency has not previously endorsed any changes to the drugmakers’ recommendations. Its current intention “is not to suggest people do anything different, but provide clinicians with flexibility for exceptional circumstances,” spokeswoman Kristen Nordlund told the New York Times.

Meanwhile, CDC Director Rochelle Walensky, M.D., on Sunday said that the federal government does not know exactly how much vaccine the U.S. government has in stock, according to CNBC. President Joe Biden has vowed that 100 million people will be inoculated within his first 100 days in office, but supply shortages are expected and may complicate matters, White House officials said.

“[T]he process to distribute the vaccine, particularly outside of nursing homes and hospitals out into the community as a whole, did not really exist when we came into the White House,” White House Chief of Staff Ron Klain told Meet the Press on Sunday.

“We’ve seen this factor all over the country where millions of doses have been distributed. About half of that has been given out,” Klain continued. “So the process of getting that vaccine into arms — that’s the hard process. That’s where we’re behind as a country, and that’s where we’re focused, in the Biden administration, on getting that ramped up.”

Pharmacies beyond CVS and Walgreens are beginning to ramp up their involvement in the vaccination campaign after federal officials opened up the field to other players. Walmart, for example, will offer Covid-19 vaccinations in seven more states, as well as in Chicago and Puerto Rico, starting this week and next, CNBC reported. The states include Georgia, Indiana, Louisiana, Maryland, New Jersey, South Carolina and Texas.

Long-term care on track

The federal vaccination campaign in skilled nursing and assisted living communities, meanwhile, appears to be chugging along. In fact, nearly all nursing homes in the federal Pharmacy Partnership for Long-Term Care program have scheduled their first COVID-19 vaccination clinics, and 88% completed the first clinic as of Jan. 21, according to CDC data. 

Pharmacy partner CVS Health Corp, for example, on Monday said it has completed administering the first round of doses at about 8,000 U.S. skilled nursing facilities, and the second round of doses should be complete in four weeks. And Walgreens said it has administered more than 1 million first-round doses at SNFs and was on track to finish by Monday. About 35,000 long-term care facilities selected Walgreens for the vaccination program.