Adverse events of COVID-19 vaccination during 2021-2022 suppressed by breakfast consumption and favorable sleeping habit among Japanese university students.

Introduction: Young adults are hesitant to receive the coronavirus disease 2019 (COVID-19) vaccination owing to concerns regarding adverse events despite the effectiveness of vaccines in preventing SARS-CoV-2 infection-associated serious illness, hospitalization, and death. Methods: 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 on the participants' physical condition after COVID-19 vaccination. Results: Focal/systemic adverse events were highly frequent among university students after receiving the COVID-19 vaccine; however, there were no life-threatening cases or hospitalizations over two years. A higher number of vaccinations (p < 0.001), female sex (p < 0.001), and lower body mass index (BMI) (p = 0.002) were associated with an increased incidence of adverse events on the day of COVID-19 vaccination or the day after vaccination. Regular breakfast consumption was significantly associated with a decreased incidence of post-vaccination itching (p = 0.019) and abdominal pain and diarrhea (p = 0.042). Sufficient sleep duration was significantly associated with a decreased incidence of post-vaccination abdominal pain and diarrhea (p = 0.042). Conclusions: High frequency of adverse events of COVID-19 mRNA-1273 among Japanese university students was reported. A higher number of shots, female sex, and lower BMI were associated with a higher incidence of adverse events. Regular breakfast and sufficient sleep were associated with fewer adverse events. This study may provide a possible solution to the worldwide problem of vaccine hesitancy.