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

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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: our study protocol was approved by the Ethics Committee of Faculty of Nursing, National and Kapodistrian University of Athens (reference number; 424, 26-10-2022) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors