Changes in the prevalences of cervical cell abnormalities and HPV infection between pre-vaccination and post-vaccination periods in Japan
We compared the prevalences of cervical abnormalities and HPV infection between the J-HERS 2011 and J-HERS 2021 study periods. The nationwide HPV vaccination program supported by both the Japanese national and local governments was implemented in the same period as the start of J-HERS 2011 (Fig. 1); the time interval between this period and the present study (J-HERS 2021) was ~10 years (range: 9 years 1 month to 12 years 1 month) (Fig. 1). There was no difference in age distribution between the two studies (Table 2). The HPV vaccination rate in J-HERS 2011 ranged from 3.6% to 6.1% (average, 4.9%), whereas the rate in the present study (J-HERS 2021) ranged from 3.8% to 53.0% (average, 20.0%) (Fig. 2). This finding suggests that HPV vaccine coverage was higher among J-HERS 2021 participants. In the J-HERS 2021 study, HPV vaccine coverage was highest in the 22- to 27-year age group; in the J-HERS 2011 study, coverage did not differ among age groups (Fig. 2).
Significant reductions in LSIL (OR, 0.22), LSIL/ASCH+ (OR, 0.38) and HSIL+ (OR, 0.28) were observed in J-HERS 2021 compared with J-HERS 2011 (Table 2), suggesting that HPV vaccination reduced LSIL by 78%, LSIL/ASCH+ by 62% and HSIL+ by 72% for 10 years after implementation of the national HPV vaccination program. Significant reductions were confirmed in 22- to 27-year and 28- to 33-year for LSIL (ORs of 0.13 and 0.13, respectively), the 16- to 21-year, 22- to 27-year, and 28- to 33-year age groups for LSIL/ASCH+ (ORs of 0.12, 0.18, and 0.25, respectively), and the OR for HSIL+ was 0.12 in the 28- to 33-year age group (Table 2). These findings suggest that HPV vaccination reduced LSIL by 87% in 22- to 27-year and 28- to 33-year age grops, LSIL/ASCH+ by 88%, 82%, and 74% in the 16- to 21-year, 22- to 27-year, and 28- to 33-year age groups; it reduced HSIL+ by 88% in the 28- to 33-year age group.
The comparison of HPV genotypes between J-HERS 2011 and J-HERS 2021 also revealed decreased prevalences of HPV16, HPV18, HPV31, and HPV58 infection, as well as a marginal reduction in HPV52 infection (Fig. 4A). There were no differences in HPV6 or HPV11, which are the target types for the quadrivalent HPV vaccine. The prevalence of high-risk HPV infection also decreased, but there were no differences in the prevalences of probable high-risk or low-risk HPV types (Fig.4B).
The reduction rates of HPV16 and HPV18 in J-HERS 2021 were 43% and 51%, respectively; the ORs were 0.57 (95% CI, 0.399–0.799) for HPV16 and 0.49 (95% CI, 0.265–0.899) for HPV18. The reduction rate of either HPV16 or HPV18 (i.e., HPV16/18) was 44% (OR, 0.56; 95% CI, 0.408–0.756), whereas the rate for HPV31/58 was 42% (OR, 0.58; 95% CI, 0.558–0.863). Among 22- to 27-year-old patients (who had the highest vaccination rate), the reduction rates were 88% for HPV16/18 (OR, 0.12; 95% CI, 0.045–0.299) and 62% for HPV31/58 (OR, 0.38; 95% CI, 0.208–0.702).