Adverse events of a third dose of BNT162b2 mRNA COVID-19 vaccine among Korean healthcare workers

Due to the urgency of controlling the coronavirus disease 2019 pandemic, coronavirus disease 2019 messenger ribonucleic acid (mRNA) vaccines have been expeditiously approved and introduced in several countries without sufficient evaluation for adverse events. We analyzed adverse events among Korean healthcare workers who received all 3 doses of the BNT162b2 mRNA vaccine. This survey was conducted among hospital workers of Inha University Hospital who had received the BNT162b2 mRNA vaccine for their first, second, third rounds, and using a diary card. The surveyed adverse events included local (redness, edema, and injection site pain) and systemic (fever, fatigue, headache, chill, myalgia, arthralgia, vomiting, diarrhea, pruritis, and urticaria) side effects and were divided into 5 grades (Grade 0 = none – Grade 4 = critical). Based on adverse events reported at least once after any of the 3 doses, the most common systemic adverse reactions were chills and headache (respectively, 62.6%, 62.4%), followed by myalgia (55.3%), arthralgia (53.4%), fatigue (51.6%), pruritus (38.1%), and fever (36.5%). The frequency and duration of adverse events were significantly greater in women (P < .05) than men. Except for redness, pruritus, urticaria, and most adverse reactions had a higher rate of occurrence after the third dose in subjects who also had reactions with the second dose. However, grade 4 adverse events did occur with the third dose in some patients, even if there were no side effects with the first and second doses. Adverse events experienced with the first and second doses of the BNT162b2 mRNA vaccine in Korean healthcare workers increased the incidence of adverse events at the time of the third dose. On the other hand, grade 4 adverse events could still occur with the third dose even though there were no side effects with the first and second doses.