COVID-19 Vaccines: CDC Guidance Update / Anaphylaxis with Moderna Vax

By Amy Orciari Herman

Edited by Susan Sadoughi, MD, and André Sofair, MD, MPH

The CDC made some changes to its COVID-19 vaccine recommendations late last week.

In particular, the agency now says that if the recommended dosing interval — 3 weeks for the Pfizer-BioNTech vaccine and 4 weeks for Moderna — can't be met, the second dose may be scheduled for up to 6 weeks after the first. Efficacy on administration beyond this window is limited, the CDC notes. Nonetheless, if the second dose is given after 6 weeks, the series does not need to be restarted. The agency continues to emphasize that the second dose should be given "as close to the recommended interval as possible."

The CDC also updated its advice regarding use of the two authorized vaccines interchangeably. The agency now says that "in exceptional situations" — for example, if the provider can't determine which vaccine the patient received the first time, or if the first-dose vaccine isn't available for the patient's second dose — "any available mRNA COVID-19 vaccine may be administered" to complete the series. In this case, the second dose should be given at least 4 weeks after the first.

In addition, the CDC and FDA on Friday published anaphylaxis data for Moderna's vaccine in MMWR. Of more than 4 million first doses administered between late December and early January, 10 cases of anaphylaxis were reported to the Vaccine Adverse Event Reporting System. This translates to 2.5 cases per million doses. All but one case occurred within 15 minutes of vaccination. None of the patients died. For comparison, early data suggested an anaphylaxis rate of 11.1 per million doses with the Pfizer-BioNTech vaccine — a rate that a CDC official characterized as "exceedingly rare."