The CDC weighs in on allergic reactions to the Pfizer COVID-19 vaccine.

Despite widely circulated media reports about allergic reactions to the Pfizer COVID-19 vaccine, there has been no official review of the numbers and types of these reactions. The CDC has now published its review of data from the vaccine adverse event reporting system (VAERS) covering nine early days of the Pfizer vaccine availability. It provided interesting data and overall was reassuring that these reactions are rare and can be managed effectively.

The CDC identified 21 cases reported by VAERS that met the criteria of “systemic allergic reactions” or anaphylaxis. This was correlated with the administration of a reported 1,893,360 first doses of the Pfizer-BioNTech COVID-19 vaccine (11.1 cases per million doses). This may actually underestimate the number of doses, given reporting of vaccine administration was delayed during this time. 

Ninety percent of the reactions occurred in women, although they received only 63% of the vaccines administered, suggesting a sexual predisposition to these reactions. There were no other demographics that seemed to identify these patients. The descriptions of these cases from the MMWR report is reproduced below.

The vast majority of these reactions (71%) occurred within 15 minutes of vaccination, which is reassuring since people are required to wait at the site for 15 minutes after receiving the vaccine. More importantly, only four of the individuals required hospitalization, and all recovered completely from the reactions. Most were treated with epinephrine as the primary medical intervention.

Of interest, 81% (17 of 21) of individuals with these reactions had a history of allergic problems with other foods, drugs, or insect stings, and seven of the individuals had experienced anaphylaxis before.  Since there was no pattern here, it may be that this is a marker of mast cell dysfunction as much as allergy. In contrast, there was no evidence that these reactions were related to any geographic location or a specific lot of the vaccine.

In summary, allergic reactions to the Pfizer COVID-19 vaccine are very uncommon and occur about 100 times less often than allergic reactions to penicillin. The mechanism of these reactions is still unknown and needs to be aggressively pursued. Locations administering COVID-19 vaccines should screen recipients for allergies to vaccine components and be able to manage anaphylaxis.

The bottom line is, however, that a general history of allergies should not de facto prevent you from receiving the vaccine. If you have questions or concerns, see your allergist!

Published by jbakerjrblog

Immunologist, former Army MD, former head of allergy and clinical immunology at University of Michigan, vaccine developer and opinionated guy.

6 thoughts on “The CDC weighs in on allergic reactions to the Pfizer COVID-19 vaccine.

  1. Jim: I received the first dose of the Pfizer vaccine and experienced a significant nose bleed within 18 hours. For what it is worth. I am fine.


  2. Dr. Baker: Would you be willing to speak to the Wayne Rotary Club? We meet weekly via Zoom every Tuesday. We would love to have you speak about the Pandemic and your blog. All Tuesdays in February are available. Could you spare 15 minutes to talk to us? Thanks for your consideration. Laura Mack, President, Rotary Club of Wayne, MI


  3. Interesting that 4 had sulfa drug allergies out of the 9 or so reporting prior drug allergies. Is this perhaps because in the overall population allergies to sulfa drugs are more common or should I be worried specifically that there may be some correlation between sulfa drug allergies and vaccine reaction? I have had hives in response to sulfa drugs in the past but no anaphylaxis. Thanks!

    Liked by 1 person

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