Is a Booster Dose of COVID-19 Vaccines Effective on Newly Dominant Omicron Subvariants Among University Students? Comparison Between BA.1 and BA.2 Dominancy.

BACKGROUND: Although the COVID-19 Omicron BA.1 subvariant was initially predominant, the BA.2 subvariant has now replaced it. Effectiveness of a booster dose vaccination for BA.2 remains unclear among university students. METHODS: We enrolled 562 Japanese university students who became a close contact and underwent polymerase chain reaction testing. We compared infection rates and cumulative incidence rates of severe fever among the students according to the COVID-19 vaccine doses received between BA.1-dominant (January 1-March 31, 2022) and BA.2-dominant (April 1-July 31, 2022) periods. RESULTS: Infection rates for BA.1 were 32% with three doses, 49% with two doses, and 68% in the unvaccinated (P=0.008). The odds ratio (OR) for infection following three doses during BA.1 was 0.46 (95% confidence interval [CI]=0.25-0.82, P=0.009). Infection rates for BA.2 were 45% with three doses, 62% with two doses, and 64% in the unvaccinated (P=0.02). The OR for infection following three doses during BA.2 was 0.50 (95% CI=0.31-0.82, P=0.006). Effectiveness of vaccine for BA.2 tended to decrease for both three (45% vs. 32%, P=0.06) and two doses (62% vs. 49%, P=0.07) compared with those for BA.1. CONCLUSIONS: Booster dose effectiveness tended to decrease but remained significant against BA.2 subvariant predominancy among Japanese university students.

Real-World Effectiveness of a Booster Dose of the COVID-19 Vaccines among Japanese University Students.

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.

Attitudes and Behavior toward COVID-19 Vaccination in Japanese University Students: A Cross-Sectional Study.

BACKGROUND: It is said that safe and effective vaccination is an important tool to end the COVID-19 pandemic. However, recent studies have reported hesitation, especially in young adults. Promoting the vaccination of university students, who represent the young adults, will lead to infection prevention measures. The purpose of this study was to clarify to compare the vaccination rates, attitudes toward vaccines, and post-vaccination behavior of students and faculty members in order to understand the actual situation of young population. METHODS: We conducted large-scale vaccination of Hiroshima University from 21 June to 18 September 2021. This cross-sectional survey was conducted via e-mail from 27 September to 3 October 2021. RESULTS: The number of second inoculations was 10,833 /14,154 students (76.5%), and 2240/2583 staff members (86.7%). Regarding the impressions after vaccination, the most common answer was "I was able to prevent worsening of the disease even if I was infected". Many students answered that their range of activities had expanded after vaccination. However, many students (n = 1799, 87.8%) answered as having "no change after vaccination" regarding infection prevention. CONCLUSION: The high vaccination rate in this survey was thought to be due to the increased sense of security and confidence in the vaccine. The fact that young adults who perform a wide range of activities are careful about infection prevention may be one of the factors that prevents the explosive spread of infection in Japan.