Life-threatening allergic reactions after COVID-19 vaccination, called anaphylaxis, do occur, but are "exceedingly rare," officials with the Centers for Disease Control and Prevention (CDC) said on a call Wednesday.

The CDC has documented 21 confirmed cases of severe allergic reactions after COVID-19 vaccinations, which averages out to a rate of 11.1 severe reactions per 1 million doses administered, according to Dr. Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases.

Of 20 patients with available data, all had recovered, the CDC noted. 

The figures were published in a new CDC report released Wednesday and are based on an initial 1.9 million doses administered in the U.S. While the agency has since documented 29 total cases, it plans to detail those cases in an upcoming report.

Most people who developed symptoms did so within 15 minutes of vaccination and 17 patients had a documented history of allergies or allergic reactions, including to medical products, foods, and insect stings.


For comparison, the rate of anaphylaxis for the flu vaccine is 1.3 cases per 1 million doses administered. While Messonnier noted that the rate of severe allergic reactions is 10 times greater for COVID-19 vaccinations, she assured that the cases are still "exceedingly rare."

Most importantly, the CDC says anyone who has an immediate or allergic reaction to the first dose of Pfizer or Moderna’s vaccine should not receive the second dose. Also, those with a known allergy to components in the vaccine, or closely related components in the vaccine, are not advised to receive the vaccine at this time.


Additionally, the CDC advises anyone with a history of an immediate allergic reaction to a vaccine, or a history of anaphylaxis due to any cause, be observed for 30 minutes after vaccination. Most individuals are observed for 15 minutes after vaccination.

Since the Pfizer and BioNTech jab saw emergency authorization from the U.S. Food and Drug Administration before the one created by Moderna did, most of the CDC's documented cases of severe allergic reactions cropped up among recipients of Pfizer’s vaccine, said Messonnier. 

That said, the federal health agency’s recommendations apply to both drug sponsors' vaccines.

"At this point, we really don’t have enough data to say that there’s any difference in the risk [between Pfizer and Moderna vaccines], and that’s why our recommendations apply to both vaccines," she said.

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CDC officials repeatedly emphasized that the known and potential benefits of COVID-19 vaccination outweigh the risk of serious consequences arising from COVID-19 disease.

"That doesn't mean, however, that we couldn't see potential serious health events in the future," Messonnier said.

"There are tremendous efforts underway right now to try to understand what might be the cause of this severe allergic reaction with both vaccines. I don't think we have anything definitive to say, there’s a lot of hypothesis about it but at this point, our recommendations for this apply to both vaccines," she added.


The information about anaphylaxis cases has not had "significant effects" on distribution plans, and, as the CDC has previously said, all vaccination sites must be properly equipped and trained should any person experience anaphylaxis following vaccination.

Echoing remarks from other top federal officials, Messonnier voiced high hopes for expedited vaccination pace in the coming weeks amid resounding criticism of a slow nationwide vaccination effort.