This paper presents the results of a series of surveys conducted from July 2021 to March 2023 to investigate the post-vaccination adverse reactions to the mRNA-1273 (Moderna) vaccine among faculty, staff, and students at Okayama University. These studies complement the official surveys conducted by the Ministry of Health, Labour and Welfare (MHLW) and provide a more representative picture of adverse reactions in the general population including large numbers of healthy young people. Pain, swelling, redness at the injection site, fever, headache, and malaise were the main adverse reactions reported. The proportion of adverse reactions was generally higher after the second vaccination and decreased with each additional vaccination. No statistically significant differences in the adverse reactions were found for males and females and those with/without a history of allergy, but a lower proportion of fever was observed in older participants and those with underlying medical conditions. We also evaluated the association between adverse reactions and antibody titers after the third vaccination and found no significant differences in antibody levels one month after vaccination. This series of studies highlights the importance of conducting surveys in diverse populations to provide a more representative picture of post-vaccination adverse reactions during a pandemic.