Declines in HPV vaccine type prevalence in women screened for cervical cancer in the United States: Evidence of direct and herd effects of vaccination.

BACKGROUND:Human papillomavirus (HPV) vaccine has been recommended in the United States since 2006 for routine vaccination of girls at age 11-12 years and through age 26 years for women not previously vaccinated. Changes in vaccine-type HPV (VT) prevalence can be used to evaluate vaccine impact, including herd effects. METHODS:We determined type-specific HPV in cytology specimens from women aged 20-29 years screened for cervical cancer at Kaiser Permanente Northwest in 2007 and in two vaccine era periods: 2012-2013 and 2015-2016. Detection and typing used L1 consensus PCR with hybridization for 37 types, including quadrivalent vaccine types (HPV 6/11/16/18). RESULTS:Among 20-24 year-olds in 2012-2013 and 2015-2016, 44% and 64% had a history of ≥1-dose vaccination. VT prevalence decreased from 13.1% in 2007 to 2.9% in 2015-2016 (prevalence ratio [PR] = 0.22; 95% confidence interval [CI] 0.17-0.29). HPV 31 prevalence was also lower in the vaccine periods compared with 2007. VT prevalence in 2015-2016 among 20-24 year-olds was lower in both vaccinated, 1.3% (PR = 0.10; 95% CI 0.06-0.16), and unvaccinated women, 5.8% (PR = 0.45; 95% CI 0.33-0.61). Among 25-29 year-olds, 21% and 32% had a history of ≥1-dose vaccination. VT prevalence decreased from 8.1% in 2007 to 5.0% in 2015-2016 (PR = 0.62; 95% CI 0.50-0.78). Non-VT high risk prevalence was higher in the vaccine periods compared with the pre-vaccine era in both age groups, however, not in 2015-2016 compared with 2012-2013. CONCLUSION:Within 9-10 years of vaccine introduction, VT prevalence decreased 78% among 20-24 year-olds and 38% in 25-29 year-olds. There were declines in both vaccinated and unvaccinated women, showing evidence of direct and herd protection.