With the spread of the Coronavirus disease 2019 (COVID-19), missing learning opportunities due to COVID-19 has been raised as a major concern for university education. We aimed to examine the effectiveness of a booster dose of COVID-19 vaccines among Japanese university students during the spread of the Omicron variant. We enrolled 249 students who became a close contact and 294 COVID-19-infected students though the Hiroshima University COVID-19 registration system. Infection rates of people in close contact with sick individuals and symptoms of infected students were examined. Close contacts who had received a booster dose showed a significantly lower infection rate (31%) compared with those with two doses (50%, p = 0.02) and the unvaccinated (71%, p = 0.002). Age- and sex-adjusted odds ratios of receipt of a booster dose vs. two doses and unvaccinated were 0.40 (95% confidence interval [CI], 0.23−0.70, p = 0.001) and 0.44 (95% CI, 0.25−0.77, p = 0.004), respectively. The incidence of severe fever (38.5°C or higher) was significantly less prevalent in those with a booster dose (16%) compared with two doses (40%, p = 0.002) and those who were unvaccinated (75%, p < 0.0001). Booster doses reduced infection rates among close-contact students and can help students to avoid missing learning opportunities.
Keywords: COVID-19; Omicron variant; booster dose; close contact; university; vaccine; vaccine hesitancy.