A study assessed the correlation between the human papillomavirus (HPV) vaccination and high-grade cervical intraepithelial neoplasia (CIN) and found that the HPV vaccine was correlated with a reduced risk of high-grade CIN.
The study followed real-life experiences of women in Denmark and compared two different birth cohorts: women born in 1983, who were never offered a free HPV vaccine, versus women born in 1993, who were offered a free HPV vaccine at age 15. The women were followed for 10 years, from age 15 to after their first screening invitation. The main outcome measure was CIN grade two or worse (CIN2+) during the follow-up period.
A total of 19,629 women born in 1983 and 26,215 women born in 1993 were identified. The 1993 cohort had a slightly higher proportion of women who had at least a high school education (59% vs. 51%). Both groups had a median age of sexual debut of 16 years, but the proportion of women whose sexual debut took place at age 14 or younger increased from 1983 (14.3%; 95% confidence interval [CI], 13.4% to 15.1%) to 1993 (18.4%; 95% CI, 17.1% to 19.7%). When surveyed in 2005, the proportion of women aged from 18 to 24 years with more than 10 sexual partners was 14.3% (95% CI, 13.4% to 15.2%); this increased in 2012 to 17.8% (95% CI, 16.7% to 19.0%). Overtime, women were less likely to report being daily smokers at age 15 (21% to 10%). In the 1983 cohort, 80% of women (n=15,748) received cervical screening coverage, compared to 76% (n=19,951) of the 1993 cohort.
The majority of women in the 1993 cohort received the vaccine (91%), compared to <0.1% of the 1983 group. Among the screened women, 4% of the 1983 cohort and 3% of the 1993 cohort presented CIN2+. High-grade CIN risk was reduced by an estimated 30% when comparing the 1993 group versus the 1983 group; the CIN2+ relative risk was 0.74 (95% CI, 0.66 to 0.82), and the CIN3+ relative risk was 0.68 (95% CI, 0.58 to 0.79).
The study was published in Acta Obstetricia et Gynecologica Scandinavica.
“Many countries may face similar challenges in the study of vaccination effects, but real‐life knowledge on impact of HPV vaccination is necessary to optimize future screening of vaccinated birth cohorts. Furthermore, the evidence of real‐life effectiveness of HPV vaccination supports the existence of public HPV‐immunization programs,” the researchers concluded.