Purpose: Approximately 70% of cervical cancers and about 50% of high-grade cervical precursor lesions are caused by human papillomavirus (HPV) types 16 and 18. Denmark introduced the quadrivalent HPV vaccine into the vaccination program for 12-year-old girls in 2009 supplemented by a first catch-up program for 13-15-year-old girls in 2008, and a second program for women up to the age of 27 years in 2012; all with high vaccination coverage. The aim of this study was to evaluate the effectiveness of the vaccine by comparing the incidence trends of cervical lesions before and after its introduction.
Methods: Incident cases of cervical lesions were identified from the nationwide Pathology Data Bank. Age-specific incidence rates were estimated for six age groups, and Poisson regression was used to calculate estimated annual percentage change (EAPC).
Results: The incidence of atypia or worse (atypia+) and cervical intraepithelial neoplasia grade 2 or worse (CIN2+) increased in all age groups in 2000-2010. After introduction of the quadrivalent HPV vaccine into the vaccination program, the incidence of atypia+ decreased significantly in women younger than 18 years (EAPC -33.4%; 95% CI -49.6; -12.0) and in 18-20-year-old women (EAPC -12.6%; 95% CI -19.3; -5.3). The incidence of CIN2+ also decreased significantly in 18-20-year-old women (EAPC -14.8%; 95% CI -21.6; -7.5) in 2010-2013, but no significant decrease was seen in older age groups.
Conclusion: The incidence of cervical lesions decreased significantly in age groups with high HPV vaccine coverage, indicating an early effect of HPV vaccination.