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While rare, the rate of anaphylaxis following COVID-19 mRNA vaccines appeared about 10 times that documented for flu shots, CDC officials said on Wednesday.

Overall, 21 cases of anaphylaxis following COVID vaccination were reported out of about 1.9 million doses given as of Dec. 23, according to an early release. That amounts to 11.1 cases per million versus an estimated 1.3 cases per million following inactivated influenza vaccine, agency officials said on a call with the media.

They noted that, as of now, 29 confirmed cases of anaphylaxis are reported with the Pfizer/BioNTech and Moderna vaccines. In addition, the officials said, the MMWR report from Dec. 14-23 focuses on the Pfizer vaccine, since the Moderna vaccine was not available until Dec. 21. Still, there is not enough data to see a difference in risk between vaccines.

No deaths from anaphylaxis have been seen to date.

Nancy Messonnier, MD, director of CDC's National Center for Immunization and Respiratory Diseases, emphasized that these events were rare and that the benefits of COVID-19 vaccination outweighed the risks. Moreover, comparing these to the numbers for flu "misses the point" when there are over 2,000 deaths from COVID-19 every day in the U.S.

"It's still a good value proposition," she said. "Even if the rate is higher than what we see after routine immunizations, anaphylaxis still remains rare."

Of the 21 cases reviewed in MMWR, 18 had documented allergies or allergic reactions to drugs, medical products, food, or insect stings, and seven had experienced anaphylaxis in the past, including one following a rabies vaccine and one following an influenza A (H1N1) vaccine.

Messonnier acknowledged the millions of people who have allergies to food or insect stings, and stressed the difference between "someone who had a mild allergic reaction in their childhood versus someone with a severe allergic reaction next week."

"A lot of people have some history of allergy to bee sting or food and the fact that people in this group had anaphylaxis ... may not mean allergic reactions put them at higher risk, but it might," she added.

Messonnier noted that CDC guidance indicates that anyone with a history of anaphylaxis for any reason should talk to their healthcare provider prior to vaccination and clinicians should exercise their judgment.

CDC officials said anyone with a history of anaphylaxis who gets the vaccine should be observed for 30 minutes afterwards, as people who previously had anaphylaxis are at risk of having it again.

The agency recently updated its interim guidance for clinicians about contraindications to the vaccine, adding that those with an immediate allergic reaction to the first vaccine should not receive a second dose.

Seventeen of the 21 cases were among those with a history of anaphylaxis, and median time from vaccination to symptom onset was 13 minutes, although around 70% of patients had symptom onset within 15 minutes. The median age of patients was 40, and 19 were women.

The MMWR report noted that female predominance had been seen earlier for immediate hypersensitivity reactions to influenza A (H1N1) vaccine. But the disproportion with COVID vaccination could simply be due to more women than men receiving the Pfizer/BioNTech vaccine, the authors said.

Nineteen patients were treated with epinephrine, 17 were treated in the emergency department, and four were hospitalized, including three in intensive care. Among 20 with available information, all were discharged home.

Also, Messonnier briefly addressed reports of healthcare workers electing not to get vaccinated, saying she was "definitely concerned" about it.

"It makes it exceedingly important that we get the correct information to healthcare workers and we quickly dispense with misinformation," she said. "We need them not only to protect themselves, but to educate their patients so everyone understands these vaccines ... have a good safety profile, they are working, and they ... can help us end this pandemic."

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