We also examined the prevalence of 3 HPV types for which there has been some evidence of cross-protection.10,11 The prevalence estimate for any HPV-31, -33, -45 in the vaccine era among all female subjects aged 14 to 19 years was unstable; there was no statistically significant decline compared with the prevaccine era. We also found no vaccine effectiveness against these 3 types among females aged 14 to 24 years in the vaccine era. Prelicensure clinical trials of both quadrivalent and bivalent vaccines investigated cross-protection against persistent infection and cervical intraepithelial neoplasia due to nonvaccine high-risk types.10,18–20 Trials of bivalent HPV vaccine found more evidence of cross-protection than did trials of 4vHPV. Other postlicensure prevalence evaluations have investigated cross-protection.16,21,22 In England and Scotland, where the bivalent HPV vaccine was introduced, decreases were observed in HPV-16, -18, as well as related types, in the vaccine era.21,22 In Australia, where 4vHPV was introduced, HPV-6, -11, -16, 18 prevalence among women aged 18 to 24 years decreased from 37.6% to 6.5%.16 For HPV-31, -33, -45, there was no statistically significant change between the prevaccine and vaccine eras; within the vaccine era, however, a significant 58% effectiveness was observed. Further analyses of NHANES data will assess changes in HPV prevalence in the United States as HPV vaccine coverage increases. However, introduction of 9vHPV will make it more difficult to evaluate changes due to potential 4vHPV cross-protection for these 3 types beyond 2015.23