C.D.C. Eases Coronavirus Vaccine Rules for ‘Exceptional Circumstances’

WASHINGTON — The Centers for Disease Control and Prevention has quietly changed its recommendations for coronavirus immunizations to give doctors the flexibility to handle “exceptional circumstances,” a spokeswoman said, even though the changes have not been studied in large clinical trials.

In guidelines posted on the agency’s website on Thursday, the C.D.C. said that patients may switch between the two authorized vaccines — one by Pfizer and BioNTech, the other by Moderna — between the first and second doses in “exceptional situations.” The C.D.C. also said patients may extend the interval between doses to six weeks from three or four if giving the second dose sooner was “not feasible.”

With the possibility of vaccine shortages on the horizon and little expectation that supply can be increased before April, the changes may offer a way to vaccinate more people — a high priority for President Biden, who outlined his national coronavirus strategy on Thursday.

Until now, the C.D.C. had cautioned against any dosing changes, saying there was no evidence for it. A C.D.C. spokeswoman, Kristen Nordlund, said the agency’s “intention is not to suggest people do anything different, but provide clinicians with flexibility for exceptional circumstances.”

Dr. Anthony S. Fauci, the president’s special adviser for the coronavirus, had repeatedly advised against delaying the second dose or making any other changes in vaccination protocol without the data to support them. But on Friday, he seemed open to delaying second doses, at least for short periods, telling CNN he took no issue with the agency’s recommendations.

“What the C.D.C. is saying, sometimes, the situation is stressed where it’s very difficult to be exactly on time,” Dr. Fauci said. “So we’re saying, you can probably do it six weeks later, namely, two additional weeks. Quite frankly, immunologically, I don’t think that’s going to make a big difference.”

This month, Britain quietly updated its vaccination playbook to allow for a mix-and-match vaccine regimen if the second dose of the vaccine a patient originally received was not available, or if the manufacturer of the first shot was not known. Some scientists questioned the move at the time, saying Britain was gambling with its new guidance.  ...