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NIH Starts Trial Looking at Rare Allergic Reactions to COVID-19 Vaccines

THURSDAY, April 8, 2021 -- A new clinical trial will investigate whether people who are highly allergic or have a mast cell disorder are at higher risk for a sudden allergic reaction to the Moderna or Pfizer COVID-19 vaccines.

"The public understandably has been concerned about reports of rare, severe allergic reactions to the Moderna and Pfizer-BioNTech COVID-19 vaccines," Anthony Fauci, M.D., director of the U.S. National Institute of Allergy and Infectious Diseases, said in a statement. "The information gathered during this trial will help doctors advise people who are highly allergic or have a mast cell disorder about the risks and benefits of receiving these two vaccines. However, for most people, the benefits of COVID-19 vaccination far outweigh the risks."

The Moderna and Pfizer COVID-19 vaccines have been given to millions of Americans. Most of the rare, severe reactions have happened to people with a history of allergies. A number of them had previously experienced anaphylaxis, the researchers noted.

The new study will enroll 3,400 people between 18 and 69 years of age. Up to 35 allergy research centers across the United States will take part, according to NIAID. By design, about 60 percent of study participants must have a history of severe allergic reactions or have been diagnosed with a mast cell disorder. The rest will not. Participants will be randomly assigned to receive either the Pfizer or Moderna shot or a placebo followed by either vaccine. About two-thirds of participants will be women, because severe allergic reactions to vaccines -- and particularly to the Moderna and Pfizer COVID-19 vaccines -- have happened in women, the researchers said. The investigators will look at how many participants in each group have a systemic allergic reaction within 90 minutes after injection.

Researchers will also look at the biological mechanism causing the reactions and whether there is a way to predict who is at most risk. Results are expected late this summer.

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