1. Allergic reactions and anaphylaxis following first dose of mRNA COVID-19 vaccines were not associated with immediate, adverse reactions following second dose.
2. Antihistamine premedication may further mitigate risk of allergic reactions.
Evidence Rating Level: 2 (Good)
After several months of messenger RNA (mRNA) COVID-19 vaccines being available in the US, allergic reactions have been reported in up to 2% of people. Anaphylaxis, on the other hand, has occurred in approximately 2.5 per 100,000 persons. This raises a question regarding safety of a second dose for those who had allergic reactions to the first dose, which would entail the two-dose regimen associated with Pfizer-BioNTech and Moderna vaccines. This multicenter, retrospective study at Brigham and Women’s Hospital, Massachusetts General Hospital, Yale School of Medicine, Vanderbilt University Medical Center, and University of Texas Southwestern Medical Center analyzed patient data from January 1, 2021 to March 31, 2021. Included patients were those with an immediate allergic reaction to a vaccine, defined as (1) symptoms within 4 hours of first dose; (2) at least 1 allergic symptom; and, (3) referral for an immunology/allergy consultation. Occurrences of anaphylaxis were scored using the Brighton and the National Institute of Allergy and Infectious Diseases/Food Allergy and Anaphylaxis Network criteria, one of which must have been met for anaphylaxis to be confirmed. Primary outcomes were related to tolerance of second vaccine dose, including no immediate symptoms or mild, transient symptoms resolved with antihistamines. A total of 189 patients experienced immediate reactions to dose one of the two possible vaccines and were included in this study (M [SD] age = 43  years, 86% female). Of these, 69% reacted to the Moderna vaccine and 31% to the Pfizer-BioNTech vaccine. Reactions across vaccines were erythema (28%), lightheadedness or dizziness (26%), tingling (24%), tightness in throat (22%), hives (21%), and shortness of breath or wheezing (21%). A total of 17% met criteria for anaphylaxis. Of the 189 patients included, 84% received a second dose and 30% of these people were premedicated with antihistamine. All of these patients tolerated the second vaccine dose, including those who initially experienced anaphylaxis. Approximately 20% reported mild, transient symptoms that resolved with antihistamines. Overall, this study demonstrates that allergic reactions and anaphylaxis do not necessarily predict reactions to a second dose of the mRNA vaccines. Though this retrospective study is limited, potential risks can be mitigated with antihistamine premedication and careful monitoring immediately following vaccine dose.
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