Declines in Human Papillomavirus (HPV)-Associated High-Grade Cervical Lesions After Introduction of HPV Vaccines in Connecticut, United States, 2008-2015

Background. Trends in human papillomavirus (HPV)-associated cervical lesions can provide an indication of vaccine impact. Our purpose was to measure trends in cervical lesions during 2008-2015 and to consider possible explanations including vaccination coverage, changes in screening for cervical cancer, and risk behaviors for acquiring HPV. Methods. Connecticut (CT) implemented mandatory reporting of cervical intraepithelial neoplasia grades 2/ 3 and adenocarcinoma in situ (cervical intraepithelial neoplasia grade 2 or higher [CIN2+]) in 2008. Trends by age and birth cohort were modeled using negative binomial regression and change-point methods. To evaluate possible explanations for changes, these trends were compared to changes in HPV vaccination coverage, cervical cancer screening, an antecedent event to detection of a high-grade lesion, and changes in sexual behaviors and Chlamydia trachomatis, an infection with similar epidemiology to and shared risk factors for HPV. Results. A significant decline in CIN2+ was first evident among women aged 21 years in 2010, followed by successive declines in women aged 22-26 years during 2011-2012. During 2008-2015, the rates of CIN2+ declined by 30%-74% among women aged 21-26 years, with greater declines observed in the younger women. Birth cohorts between 1985 and 1994 all experienced significant declines during the surveillance period, ranging from 25% to 82%. Ecological comparisons revealed substantial increases in HPV vaccination during this time period, and more modest reductions in cervical cancer screening and sexual risk behaviors. Conclusions. The age and cohort patterns in our data suggest that declines in CIN2+ during 2008-2015 are more likely driven by HPV vaccination, introduced in 2006, than by changes in screening or risk behavior.