Skip to content

This COVID Vaccine Side Effect More Common Than Thought, Says Study

But it's "not scary," says the author of a new study.
FACT CHECKED BY Alek Korab

More people had a severe allergic reaction after getting an mRNA COVID vaccine than previously believed, a new study has found. According to a research letter published in JAMA on March 8, about one in 4,000 people in one sample group experienced anaphylaxis, a swelling of the throat that can be fatal, after receiving the vaccines manufactured by Pfizer or Moderna. But all recovered completely. It's important to note that even with these new stats, the chances of anyone having the reaction remains "extremely low," say researchers. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had Coronavirus.

2% Had Acute Allergic Reactions, Say Researchers

In the study, researchers looked at 64,900 employees of the Mass General Brigham health system who got their first dose of a Pfizer or Moderna vaccine. Forty percent received the Pfizer shot, and 60% Moderna. Acute allergic reactions were reported by 2% of them, and 16 people experienced anaphylaxis.  

Of those 16, nine were treated with epinephrine (EpiPen) and three who had a history of anaphylaxis chose not to seek care. Only one person was admitted to intensive care. Everyone was ultimately OK. 

The anaphylactic reactions started 17 minutes after administration of the shot, on average. The mean age was 41, and 15 of the 16 people were female. Sixty-three percent had a prior allergy history, and 31% had a prior history of anaphylaxis.

Severe Reactions About 22 Times Higher Than CDC Report

"Severe reactions consistent with anaphylaxis occurred at a rate of 2.47 per 10,000 vaccinations," the study authors wrote. That's about 22 times the rate that was reported by the CDC in January.

"The incidence rate of confirmed anaphylaxis in this study is larger than that reported by the Centers for Disease Control and Prevention," the researchers wrote. "However, the overall risk of anaphylaxis to an mRNA COVID-19 vaccine remains extremely low and largely comparable to other common health care exposures."

They added: "Given that approximately 5% of adults have severe food allergy histories and 1% of adults have severe drug allergy histories, this MGB employee cohort likely included almost 4,000 individuals with severe food or medication allergy histories who were safely vaccinated."

Kelly Blumenthal, an immunologist who studies drug allergies and led the study, said the CDC relied on self-reporting from people who'd gotten the vaccine, while her team studied a specific group and had access to all their data. "Sometimes there is key information missing in [Vaccine Adverse Event Reporting System] reports or missing records," she tweeted, adding that there could be "differences potentially based on geography or employee demographics… 2.47 per 10,000 is NOT scary. These are great vaccines and all with anaphylaxis recovered."

How to Survive This Pandemic

As for yourself, do everything you can to prevent getting—and spreading—COVID-19 in the first place: Wear a face mask, get tested if you think you have coronavirus, avoid crowds (and bars, and house parties), practice social distancing, only run essential errands, wash your hands regularly, disinfect frequently touched surfaces, and to get through this pandemic at your healthiest, don't miss these 35 Places You're Most Likely to Catch COVID.

Filed Under