ABSTRACT
Objectives: Effective vaccines are prioritized to curtail the transmission and burden of coronavirus disease 2019. Nevertheless, monitoring the safety of vaccines is crucial. As Thailand began the ChAdOx1 nCoV-19 vaccination, our study examined the acute adverse effects and associated factors after the first dose of vaccination. Methods: A mobile self-report questionnaire was employed to assess the rates and types of different side-effects within 3 days of the first dose of ChAdOx1 nCoV-19 vaccine administration. The risk factors associated with these side-effects were analyzed. Results: In total, 774 participants were included in the survey, with a mean (± standard deviation) age of 49.5 (± 17.2) years. The majority (57.8%) were females, and 59.1% were anxious before the vaccination. Side-effects after the vaccination were a common occurrence (65.2%), but most (42.6%) were mild. Side-effects were significantly associated (odds ratio [95% confidence interval]) with younger age (4.32 [2.26-8.23]; p < 0.001; age < 30 years vs ≥ 60 years), female sex (1.66 [1.19-2.30], p = 0.003), anxiousness (2.10 [1.06-4.13]; p = 0.033; moderate-severe anxiousness vs none), and allergic disease (2.60 [1.07-6.31]; p = 0.035). Conclusions: After the ChAdOx1 nCoV-19 vaccination, most acute adverse effects were mild and often noted among participants with younger age, female sex, anxiousness, and allergic disease.