Human papillomavirus vaccine to prevent cervical intraepithelial neoplasia in Japan: A nationwide case-control study.

Cervical cancer remains among the most common cancers in women worldwide and can be prevented by vaccination. The Ministry of Health, Labour and Welfare of Japan suspended the active recommendation of regular HPV vaccines in 2013 due to various symptoms including chronic pain and motor impairment. This nationwide case-control study from April 2013 to March 2017 targeted women aged 20-24 years old at cervical screening. We compared HPV vaccination exposure between those with abnormal and normal cytology. Abnormal cytology were classified based on the results of histological test and 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 2,483 cases and 12,296 controls (one-to-five matching) were eligible in 30 municipalities in Japan. The distribution of histological abnormalities among cases were 797 CIN1 (including dysplasia) (32.1%), 165 CIN2 (6.7%), 44 CIN3 (1.8%), and eight squamous cell carcinoma (SCC) (0.3%). The ORs of HPV vaccination compared with no vaccination for abnormal cytology, CIN1+, CIN2+, and CIN3+ versus controls was 0.42 (95% CI, 0.34-0.50), 0.42 (95% CI, 0.31-0.58), 0.25 (95% CI, 0.12-0.54), and 0.19 (95% CI, 0.03-1.15), respectively, equating to a vaccine effectiveness of 58.5%, 57.9%, 74.8%, and 80.9%, respectively. Eight patients had SCC, none were vaccinated. This nationwide case-control study in Japan demonstrated a substantial risk reduction in abnormal cytology and CIN among women who did versus those who did not receive HPV vaccination.