Objective: Evaluate the efficacy of catch-up HPV vaccination in sexually active young women and the potential impact of HPV vaccines on the practice of organized screening.
Sample: (1) Women enrolled in the Future II study and (2) from a separate population-based study in Iceland.
Methods: (1) Analysis of cytological and histological results and colposcopic examinations among 710 women, aged 18-23, with less than five sexual partners, irrespectively of baseline HPV status at enrolment. (2) The impact on screening practice as determined by evaluating the distribution of 12 oncogenic HPV types in 582 cervical intraepithelial lesions (CIN 2-3) and cancer cases.
Main outcome measures: (1) Distribution of evaluated parameters according to age at enrolment. (2) Age distribution of four HPV groups, within age classes and HPV groups: mean time to development of lesions, mean time to development of CIN 2-3+, cumulative frequency for CIN 2-3+ lesions after the last normal smear.
Results: (1) After an average 52 months of post-enrolment follow-up, significant reductions in all evaluated parameters were observed in women aged 18-19 at enrolment. (2) Among women <25 years, the proportion of cases with only HPV 16/18 was significantly lower and the proportion containing HPV16/18 plus > or =1 out of 10 non-vaccine HPV types (31/33/45/52/58/35/39/51/56/59) was higher than at age 25-49. The proportion of cases containing only the non-vaccine types was the same within all age groups. Cases with HPV 16/18 and some non-vaccine types decreased significantly with age and accumulated more slowly after the last negative smear.
Conclusions: Catch-up vaccination of younger women should be considered in the context of sexual practices and the effects of prevalent disease on observed vaccine efficacy. Current data do not support a change in the lower age limit or screening intervals for women.