Just 0.025 percent of staff from Massachusetts General Hospital and Brigham and Women's Hospital experienced anaphylaxis after receiving Pfizer or Moderna COVID-19 vaccines, according to a study published March 8 in JAMA.
Researchers from Massachusetts General Hospital and Brigham and Women's Hospital, both based in Boston, sent survey links to 64,900 of the hospitals' employees who received either a Pfizer or Moderna COVID-19 vaccine from Dec. 16 to Feb. 12. Both Pfizer and Moderna's vaccines use mRNA, which means they mimic infection in the body by carrying the genetic instructions for cells to produce antigens that fight COVID-19.
Acute allergic reactions, which were defined on the survey as itching, rash, hives, swelling, and/or respiratory symptoms, occurred in 2.10 percent of respondents, but anaphylaxis occurred in only 0.025 percent.
Anaphylaxis occurred in 16 employees who received Moderna's vaccine and seven employees who received Pfizer's vaccine. Among these 23 people, the mean age was 41. All recovered without experiencing shock or requiring endotracheal intubation.
The mean time from vaccination to anaphylaxis onset was 17 minutes. One patient required intensive care, and 56 percent received intramuscular epinephrine to steady their breathing.
Ninety-seven percent of the employees who experienced anaphylaxis were women, 63 percent had an allergy history and 31 percent previously had anaphylaxis.
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