Effect of vaccine booster dose on coronavirus disease 2019 prevention by age group: Analysis of data collected at polymerase chain reaction centers in Hiroshima Prefecture, Japan

For three years, the world has faced the coronavirus disease (COVID-19) pandemic, and vaccination against severe acute respiratory syndrome coronavirus 2 remains the best defense. In Japan, vaccination with a booster dose started in early December, with healthcare workers receiving priority, followed by elderlies aged > 65 years. We aimed to assess the effectiveness of vaccine boosters in preventing infection in various age groups of Japanese people in Hiroshima. A pre-administered questionnaire, the J-SPEED-style COVID-19 polymerase chain reaction (PCR) center version, was used to collect data from PCR centers in Hiroshima Prefecture between February 1, 2022 and March 17, 2022. The highest infection rate was observed in those aged between 10 and 19 years (6.0%), whereas the lowest infection rate was observed in those aged 45–64 years and > 65 years (3.3%). For all age groups, three doses of the vaccine provided lower infection rates than two doses. Elderlies aged > 65 years with booster doses (odds ratio [OR] = 0.499, 95% confidence interval [CI] = 0.400–0.622) were less infected compared to the same groups who received two doses, followed by those aged 45–64 years (OR = 0.663, 95% CI = 0.558–0.788) and 20–44 years (OR = 0.758, 95% CI = 0.655–0.877). In general, those aged > 65 years who received three doses (OR = 0.499, 95%CI = 0.400–0.622) were less likely to be infected with COVID-19 than those aged < 65 years (OR = 0.674, 95%CI = 0.604–0752). We analyzed the association between vaccination status and infection status; therefore, we recommend future research using data on the exact vaccination date and infection status.