Human papillomavirus vaccine to prevent CIN3 or worse (CIN3+): A nationwide case-control study in Japan.

An increase in cervical cancer incidence has been reported in Japan. The Ministry of Health, Labor, and Welfare of Japan has resumed the active recommendation of regular HPV vaccines in 2022. In Japan, the preventive effect of CIN3+ in the real world has not yet been demonstrated in age-adjusted cohort or case-control studies. This study aimed to estimate the effect of the HPV vaccine against CIN3+ in Japanese women. This nationwide case-control study from April 2013 to March 2020 targeted women aged 20-26 years old at the time of cervical screening. We compared HPV vaccination exposure between those with abnormal and those with normal cytology. Abnormal cytology was classified into cervical intraepithelial neoplasia (CIN)1+, CIN2+, and CIN3+. We calculated the odds ratio (OR) and 95% confidence interval (CI) of the above endpoints and vaccination exposure using the conditional logistic regression model and estimated vaccine effectiveness using the formula (1 -OR) × 100. A total of 2790 cases and 13,990 controls (one-to-five matching) were eligible in 37 municipalities in Japan. In this study, 61 CIN3 (2.2%) and 10 squamous cell carcinomas (SCC) (0.4%) were found. The OR for CIN3+ versus controls was 0.14 (95% CI, 0.03-0.75), equating to a vaccine effectiveness of 86%. Of the 10 patients who had SCC none were vaccinated. This nationwide case-control study in Japan demonstrated a substantial risk reduction in CIN3+ among women who did versus those who did not receive HPV vaccination.