Age at first sexual intercourse among young women with invasive cervical cancer: implications for routine vaccination against human papillomavirus in Japan.

Abstract

To the Editor The Japanese government resumed proactive recommendation of human papillomavirus (HPV) vaccination in April 2022 and has recently decided to introduce the 9-valent HPV vaccine to the routine immunization program from April 2023. In Japan, the 9-valent HPV vaccine is estimated to provide ~90% protection against both cervical cancer and precancer (1). HPV infection rates increase soon after the first sexual intercourse (2) and HPV vaccines cannot treat pre-existing HPV infections or HPV-related diseases (3). Therefore, immunization against HPVs should be completed before first sexual intercourse. Data regarding age at first sexual intercourse, especially among women who develop cervical cancer and precancer, are crucial to optimize the HPV vaccination strategy. We previously reported complete protection against HPV16/18-positive cervical precancer among Japanese girls vaccinated before age 15 years or first sexual intercourse and higher HPV vaccine effectiveness among those vaccinated at age ≤ 18 years, outside clinical trial settings (4). This is consistent with real-world studies from other countries reporting greater effectiveness of HPV vaccination at younger ages (5–9). Because the effectiveness of HPV vaccination is highly dependent on age at the first immunization, the target age in routine vaccination programs is very important to maximize the efficacy of HPV vaccines. HPV vaccination is recommended by the World Health Organization for routine immunization in girls aged 9–14 years in most countries (Fig. 1) (10–13). However, adolescents aged 15–16 years are also included as a target population for the routine vaccination program in Japan.