Prevalence and risk factors of adverse effects after the first COVID-19 booster dose: evidence from Greece

Abstract Background In general, COVID-19 vaccines are safe and effective, but minor adverse effects are common. Objective To estimate the prevalence of adverse effects after the first COVID-19 booster dose, and to identify possible risk factors. Material and methods We conducted a cross-sectional study with a convenience sample in Greece during November 2022. We measured several adverse effects after the booster dose, such as pain at the injection site, swelling at the injection site, fatigue, muscle pain, headaches, fever, chills, nausea, etc. We considered gender, age, chronic disease, self-assessment of health status, COVID-19 diagnosis, and self-assessment of COVID-19 course as possible predictors of adverse effects. Results In our sample, 96% developed at least one adverse effect. Half of the participants (50.2%) developed one to five adverse effects, 35.9% developed six to ten adverse effects, and 9.5% developed 11 to 16 adverse effects. Mean number of adverse effects was 5.5. The most frequent adverse effects were pain at the injection site (84.3%), fatigue (70.8%), muscle pain (61%), swelling at the injection site (55.2%), headache (49.8%), fever (42.9%), and chills (41%). Females developed more adverse effects than males (p<0.001). Also, we found a positive relationship between severity of COVID-19 symptoms and adverse effects of COVID-19 vaccines (p=0.005). Moreover, younger age was associated with increased adverse effects (p<0.001). Conclusions Almost all participants in our study developed minor adverse effects after the booster dose. Female gender, worse clinical course of COVID-19, and decreased age were associated with increased adverse effects.