Second Dose of COVID-19 mRNA Vaccine Found Safe After Reaction to First

As much as 2% of vaccine recipients have reported anaphylaxis following their first shot.

A recent study conducted by investigators from Massachusetts General Hospital, in collaboration with Vanderbilt University Medical Center, the University of Texas Southwestern Medical Center and the Yale School of Medicine, has found that a second dose of COVID-19 mRNA vaccine is safe for those who experienced an allergic reaction to the first dose.

Results from the study were published in the journal JAMA Internal Medicine.

“This multisite US study supports the safety of Pfizer-BioNTech or Moderna vaccine second dose administration in patients who report immediate and potentially allergic reactions after the first dose,” the authors wrote. “Second dose tolerance following reactions to the first dose argues that either many of these initial reactions are not all truly allergic reactions, or supports an allergic, but non–immunoglobulin E–mediated mechanism in which symptoms can typically be abated with premedications.”

For the study, the team of investigators combined data from their hospital from patients who sought out care by an allergy specialist due to a reaction from the first dose of an mRNA COVID-19 vaccine.

Included in the study were 189 patients, of which 159 went on to receive a second dose.

Findings from the study showed that 17% of the study participants experienced anaphylaxis after their first dose of a vaccine. Of the 159 patients who went on to receive their second dose, all of them tolerated a second dose.

Additionally, 32 of the patients who received their second dose reported immediate and potentially allergic symptoms associated with the second dose that were self-limited, mild, and/or resolved with antihistamines alone.

"One important point from this study is that these immediate onset mRNA vaccine reactions may not be mechanistically caused by classic allergy, called immediate hypersensitivity or Ig-E-mediated hypersensitivity. For classic allergy, re-exposure to the allergen causes the same or even worse symptoms," Kimberly G. Blumenthal, co-senior author on the study said. "After first dose reactions, allergy specialists may be useful to help guide risk/benefit assessments and assist with completion of safe vaccination.”