Human papillomavirus vaccine effectiveness by age at first vaccination among Japanese women

Abstract

In Japan, the National Immunization Program against human papillomavirus (HPV) targets girls aged 12-16 years, and catch-up vaccination is recommended for young women up to age 26 years. Because HPV infection rates increase soon after sexual debut, we evaluated HPV vaccine effectiveness by age at first vaccination. Along with vaccination history, HPV genotyping results from 5795 women younger than 40 years diagnosed with cervical intraepithelial neoplasia grade 2-3 (CIN2-3), adenocarcinoma in situ (AIS), or invasive cervical cancer were analyzed. The attribution of vaccine-targeted types HPV16 or HPV18 to CIN2-3/AIS was 47.0% for unvaccinated women (n = 4297), but 0.0%, 13.0%, 35.7%, and 39.6% for women vaccinated at ages 12-15 years (n = 36), 16-18 years (n = 23), 19–22 years (n = 14), and older than 22 years (n = 91), respectively, indicating the greater effectiveness of HPV vaccination among those initiating vaccination at age 18 years or younger (P