July 26, 2021

Safety of second dose of COVID-19 vaccines after first-dose allergic reactions

By: Judy Mathias

Editor's Note

This multisite US study, led by researchers at the Massachusetts General Hospital, Boston, supports the safety of administering a second dose of the Pfizer-BioNTech or Moderna COVID-19 vaccine in patients who experience allergic reactions to the first dose.

Of 189 patients who participated in the study, 130 (69%) had reactions to the first dose of Moderna, and 59 (31%) had reactions to the first dose of Pfizer-BioNTech vaccines.

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The most frequent reactions were flushing or erythema, dizziness or lightheadedness, tingling, throat tightness, hives, and wheezing or shortness of breath, with 32 (17%) of those reactions meeting anaphylaxis criteria.

A total of 159 (84%) patients received a second dose—antihistamine premedication was given to 47 (30%). All 159, including 19 patients who had first-dose anaphylaxis, tolerated the second dose. Immediate and potentially allergic symptoms were reported by 32 (20%) after the second dose, but they were mild, self-limited, and/or resolved with antihistamines.

Second dose tolerance after reaction to the first dose argues that either many of the initial reactions were not all truly allergic reactions, or supports an allergic, but non-immunoglobulin E-mediated, mechanism in which symptoms can be abated with premedications, the researchers note.


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