ABSTRACT
Despite the evidence of effectiveness of vaccines in preventing SARS-CoV-2 infection-associated serious illness, hospitalization, and death, there is some hesitation towards COVID-19 vaccination in young adults because of concerns regarding adverse events. A retrospective cohort study was conducted in Gifu University students receiving the mRNA-1273 vaccine and boosters to elucidate the real incidence of adverse events and factors that prevent them. We examined the adverse events and identified potential risk factors through a self-administered questionnaire reporting their physical condition after COVID-19 vaccination. A higher number of vaccinations, female sex, and low body mass index were significantly associated with the occurrence of adverse events on the day of or after receiving the COVID-19 vaccine. Regular breakfast consumption was significantly associated with a decreased incidence of post-vaccination itching, abdominal pain, and diarrhea. Sufficient sleep duration was significantly associated with a decreased incidence of post-vaccination abdominal pain and diarrhea. Focal/systemic adverse events were highly frequent among university students after receiving the COVID-19 vaccine, with no life-threatening cases or hospitalizations. A higher number of vaccinations, female sex, and lower body mass index were associated with an increased incidence of adverse events. Contrastingly, regular breakfast and sufficient sleep were associated with fewer adverse events.