Acute allergic reactions occurred at 2.10%, but anaphylaxis in only 0.025% of employees at two Boston hospitals who received their first dose of the Pfizer-BioNTech or Moderna COVID-19 vaccine, according to a research letter published yesterday in JAMA.
Scientists from Massachusetts General Hospital and Brigham and Women’s Hospital administered research links by email, text, phone and smartphone app to 64,900 employees who received a dose of one of the two coronavirus mRNA vaccines on December 16, 2020 on February 12, 2021.
The mRNA vaccines “teach” human cells to make a harmless part of the SARS-CoV-2 spike protein to trigger an immune response to the virus. The authors noted that people with a history of life-threatening reactions, or anaphylaxis, to allergens, such as those in a vaccine, often hesitate to receive vaccines, which can complicate efforts to end the pandemic.
A total of 25,929 employees (40%) received the Pfizer vaccine, while 38,971 (60%) received the Modern vaccine. Eighty-one percent returned at least one symptom survey, which was sent every day for 3 days after vaccination.
Among all vaccinated employees, 1,365 (2.10%) reported acute allergic reactions, defined in the survey as itching, skin rash, hives, swelling and / or respiratory symptoms. More vaccinees from Moderna (2.20%) reported symptoms than vaccinates from Pfizer (1.95%).
Previous anaphylactic episodes
A review of medical records identified anaphylaxis in 16 workers (0.025%) (9 [0.023%] with the Moderna vaccine and 7 [0.027%] with the Pfizer vaccine). The average age of vaccinees diagnosed with anaphylaxis was 41 years, 94% were women, 63% had a history of allergy and 31% had already had anaphylaxis.
The average time from the start of vaccination to anaphylaxis was 17 minutes. One patient required intensive care, 56% received intramuscular epinephrine (to facilitate breathing) and all recovered without being shocked or requiring endotracheal intubation. Three workers with a history of anaphylaxis did not seek medical attention. The mechanism of anaphylaxis occurrences in the study is unknown.
The Centers for Disease Control and Prevention previously reported an incidence of anaphylaxis of 2.5 to 11.1 per million doses, most of them in people with a history of allergy, the authors noted.
“The incidence rate of anaphylaxis confirmed in this study is higher than that reported by the Centers for Disease Control and Prevention based on spontaneous and passive reporting methods,” they wrote. “However, the overall risk of anaphylaxis for a COVID-19 mRNA vaccine remains extremely low and broadly comparable to other common healthcare exposures.”
Although the majority of those vaccinated with anaphylaxis had a history of allergy, the researchers noted that since about 5% of US adults have severe food allergies and 1% have severe allergies to medications, the group of employees studied must have included about 4,000 workers with a history of anaphylaxis who were vaccinated without related adverse events.
“In this prospective cohort of healthcare workers, 98% did not show any symptoms of an allergic reaction after receiving a COVID-19 mRNA vaccine,” wrote the authors.