Allergic reactions to mRNA-based COVID-19 vaccines focus of new NIH trial

The US National Institutes of Health (NIH) on Wednesday announced the start of a Phase II trial to determine why some people have suffered allergic reactions after being given Moderna's mRNA-1273 or Pfizer and BioNTech's BNT162b2 coronavirus vaccines. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases, said the information gathered during the 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."

The two-dose inoculations, both of which are based on mRNA, were the first to be authorised for emergency use in the US to protect against COVID-19. They have already been administered to millions of Americans, and the NIH says most of the rare, severe allergic reactions to them occurred in people who have a history of allergies, with a "substantial number" having previously experienced anaphylaxis as well.

The new NIH study will enroll 3400 adults ages 18 to 69 years across the US, with about 60% having either a history of severe allergic reactions or a diagnosis of a mast cell disorder (Group 1), while the remainder will not (Group 2). The allergies can be related to food, insect stings or allergen immunotherapy and require epinephrine treatment, or may involve immediate allergic reactions to a vaccine or to one or more drugs. The NIH noted that as severe allergic reactions to the two COVID-19 vaccines, and to vaccines in general, have occurred mainly in women, two-thirds of the study participants will be female.

Results due end of summer

Volunteers in each group will be assigned at random to receive either BNT162b2, mRNA-1272, a placebo followed by BNT162b2 or a placebo followed by mRNA-1273. Ultimately, all study subjects will receive a full two-dose course of either the Pfizer-BioNTech or Moderna vaccines. Investigators will assess the proportion in each group who have a systemic allergic reaction within 90 minutes after injection with either dose of BNT162b2 or mRNA-1273. Results are expected in late summer.

According to a paper published earlier this year in JAMA Insights, the rate of reported anaphylaxis was 4.7 cases per million doses of BNT162b2, and 2.5 cases per million doses of mRNA-1273, based on more than 17.5 million shots of the two vaccines administered from about mid-December to mid-January. The US Centers for Disease Control and Prevention advises COVID-19 vaccination even for people with a history of severe allergic reactions, provided those were not triggered by injectable medications.

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