The NIH’s National Institute of Allergy and Infectious Diseases has begun a phase 2 study to evaluate the risk of allergic reactions to the Moderna and Pfizer/BioNTech COVID-19 vaccines in patients who are severely allergic or have a mast-cell disorder.

The trial, which will be conducted at up to 35 academic allergy research centers across the U.S., will enroll 3,400 adults aged 18 to 69 years old. Approximately 60 percent of the study participants will consist of people with a history of severe allergic reactions or a diagnosis of a mast-cell disorder, a disease that predisposes patients to life-threatening reactions, NIH said.

Specifically, those individuals must have a history of reactions related to food, insect stings or allergen immunotherapy that required epinephrine, or immediate reactions to a vaccine or drug. The remaining 40 percent will include participants with no history of such conditions.

For each patient group, approximately two-thirds of participants will be female, as most severe allergic reactions to vaccines, including the Moderna and Pfizer/BioNTech inoculations, have occurred in women, NIH said.