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Researchers are enrolling participants in a study to determine whether people with severe allergies or a mast cell disorder are at higher risk of allergic reactions to the COVID-19 mRNA vaccines than those without allergies.

The clinical trial, which will enroll 3,400 adults ages 18 to 69 at up to 35 centers across the United States, launched on April 7.

“The public understandably has been concerned about reports of rare, severe allergic reactions to the Moderna and Pfizer-BioNTech COVID-19 vaccines,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, the trial’s sponsor.

“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,” said Fauci.

Since the Pfizer-BioNTech and Moderna COVID-19 vaccines rollout began in December 2020, millions of Americans – including those with severe allergies to foods, drugs and insect venom – have received the vaccines without any problems.

But reports of rare cases of anaphylaxis have led to questions about whether people with a history of allergies or mast cell disorders are more likely to have allergic reaction to the vaccines, and if so, why. The majority of anaphylactic reactions have been reported in women and in people with a history of allergies to a wide range of triggers, including foods, drugs, injectable medications or contrast dye.

Most Subjects Will Be Women

The multi-center trial will enroll over 2,000 people adults with a history of severe allergic reactions or mast cell disorder, a condition in which people experience episodes of anaphylaxis without a known allergy trigger. A control group will include nearly 1,400 people without allergies. Two-thirds of participants will be women.

Photos: NIAID and University of Michigan Dr. Anthony Fauci and Dr. James Baker

Participants will be randomly assigned to receive either the Pfizer vaccine, the Moderna vaccine, or a placebo during their first visit. (The first part of the study is “blinded,” so that neither study subjects nor researchers know who got the actual vaccine with the first shot.)

Everyone gets an actual vaccine shot on the second visit, and three days after receiving that, participants will learn which dose they initially received.

During a visit for a shot, the participants will be observed for 90 minutes by allergists who are able to treat any reactions. Blood, urine and nasal swabs will be taken before each dose is given, and blood and urine will be taken after each shot.

If there are any reactions, researchers will analyze the samples and run genetic tests to try to determine what type of reaction occurred, and whether certain genetic characteristics may make people more prone to reactions, said Dr. James R. Baker, co-chair of the study and director of the Mary H. Weiser Food Allergy Center at the University of Michigan.

Participants in the placebo group for the first shot will have their second dose scheduled at the appropriate interval, which is three weeks for the Pfizer vaccine and four weeks for Moderna.

“Everyone in this study will receive either the Pfizer or the Moderna vaccines,” Baker says. Results of the study are expected in late summer.

How Can I Enroll?

The study includes sites in 20 states, including: Arizona, Arkansas, California, Colorado, Florida, Georgia, Illinois, Iowa, Maryland, Massachusetts, Michigan, Missouri, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Texas, Virginia and Wisconsin. For contacts and locations, visit this page (open the ‘show study locations’ tab). Not all centers have yet begun enrolling, so check back for updates.  

Participants in the allergy group must have a history within the last five years of a severe reaction to foods, allergen immunotherapy, or insect venom; an immediate allergic reaction to two or more drugs; or a convincing clinical history, including a positive skin test, of a reaction to a drug or vaccine. The study will also include people diagnosed with a mast cell disorder.

People in the non-allergy group must have no history of allergic disorders, including allergic asthma, rhinitis, eczema or chronic hives.

Exclusion criteria:
Among those excluded are: people who have taken a biologic therapy within six months of the trial, anyone who has used oral steroids within 28 days, or anyone who has recently had COVID.

For more information on the study:
Visit, the study identification number is NCT04761822.

Related Reading:
Few Severe Reactions to COVID-19 Vaccines, But Women Most Affected
FAQ on: Allergy Concerns and the mRNA COVID-19 Vaccine


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