How frequent are acute reactions to COVID-19 vaccination and who is at risk?

INTRODUCTION: Our objective was to describe and compare self-reported side effects of COVID-19 vaccines in the USA. METHODS: A web-based registry enrolled volunteers who received a COVID-19 vaccine between March 19–July 15, 2021. We collected self-reported short-term side effects, medical consultation, hospitalization, and quality of life impact following completed vaccination regimens (Pfizer, Moderna, J&J). RESULTS: We recruited 6,966 volunteers who completed their full course of vaccination (median age 48 years, IQR 35.0–62.0; 83.6% female): Pfizer 3,486; Moderna 2,857; J&J 623. Few (3.1%) sought medical care for post-vaccination side effects. Hospitalization (n = 17; 0.3%) and severe allergic reactions (n = 39; 0.6%) also were rare. Those with autoimmune disease or lung disease were approximately twice as likely to seek medical care (adjusted odds ratio (aOR) 2.01, 95% CI:1.39; 2.92 and aOR 1.70, 95% CI: 1.12; .58 respectively). 92.4% of participants reported ≥ 1 side effect (median 3), with injection site reactions (78.9%), fatigue (70.3%), headache (49.0%) reported most frequently. More side effects were reported after the second dose of two-dose vaccines (medians: 1 vs. 2 for Pfizer and 1 vs. 3 for Moderna for first and second doses respectively) versus 3 for J&J's single-dose vaccine. For the employed, the median number of workdays missed was one. Diabetics and those vaccinated against influenza were substantially less likely to report 3 or more symptoms (aOR 0.68, 95% CI: 0.56;0.82] and aOR 0.82, 95% CI: 0.73;0.93, respectively). DISCUSSION: The total side effect burden was, not unexpectedly, greater with two-dose regimens but all three vaccines appear relatively safe. Very few subjects reported side effects serious enough to warrant medical care or reported post-vaccination hospitalization. While these findings do not address possible long-term effects, they do inform on their short-term safety and tolerability and will hopefully provide some reassurance and positively inform the benefit-risk and pharmacoeconomic assessment for all three vaccines. See Clinicaltrials.gov NCT04368065.