Incidence and Factors Associated with Self-Reported Skin Symptoms of Allergic Reactions to COVID-19 Vaccines.

Background: Few reports exist regarding the incidence and factors associated with allergic reactions to COVID-19 vaccines during post-marketing surveillance, especially for inactivated whole virus or viral vector vaccines. We aimed to determine the incidence and factors associated with self-reported allergic reactions to COVID-19 vaccines in the Thai population. Methods: A cross-sectional case-control study was conducted via telephone-based interviews. Cases were defined as physician-confirmed, self-reported vaccine recipients diagnosed with non-severe immediate allergic reactions, anaphylaxis, or delayed allergic reactions. Controls were randomly sampled from vaccinated individuals who reported no adverse events and were matched by the type of vaccine (1 case:2 controls). Demographic information and the history of atopic diseases were collected in both groups. Conditional logistic regression analysis was used to explore associated factors. Results: Among 215,079 vaccine doses administered, the incidence of self-reported skin symptoms of allergic reactions was 1821 events (0.85%). The risk factors for allergic reactions included age < 60 years (aOR 3.53; 95% CI:1.43-8.70; p = 0.006), female sex (aOR 8.33; 95% CI: 4.35-15.94; p < 0.001), a personal history of allergic rhinitis (aOR 4.32; 95% CI: 2.43-7.69; p < 0.001), atopic dermatitis (aOR 4.27; 95% CI: 1.74-10.47; p = 0.002), food allergies (aOR 6.53; 95% CI: 2.42-17.61; p < 0.001), and a family history of allergic disease (aOR 2.14; 95% CI: 1.12-4.08; p = 0.021). Conclusions: COVID-19 vaccines showed a low incidence of self-reported allergic reactions, which were more likely to occur in younger individuals, females, and those with a history of atopic diseases.