Who's Not Protected in the Herd? Factors Associated with Vaccine-Type HPV in Unvaccinated Women

Evidence suggests that vaccine-type human papillomavirus (HPV) prevalence may decrease in unvaccinated women after HPV vaccine introduction, indicating herd protection. The aim of this study was to determine factors associated with vaccine-type HPV (i.e. absence of herd protection) after vaccine introduction. We conducted three cross-sectional studies from 2006-2014 (n = 1180): wave 1 (2006-2007), wave 2 (2009-2010), and wave 3 (2013-2014). Participants were recruited from a hospital-based teen health center and a community health department. We recruited 13-26 year-old young women; those included in this analysis had not received an HPV vaccine. The outcome measure was infection with at least one vaccine-type HPV (HPV6, 11, 16, 18). Multivariable logistic regression demonstrated that in wave 1 (before vaccine introduction), history of anal intercourse (OR = 1.8, 95% CI = 1.1-3.0), age 18-21 vs 13-17 years (OR = 2.1, CI = 1.2-3.6), and Black/multiracial vs White race (OR = 1.8, CI = 1.1-3.0) were associated with vaccine-type HPV in unvaccinated women. In wave 2, no variables were associated with HPV. In wave 3, sexually transmitted infection history (OR = 3.6, CI = 1.3-9.7) was associated with HPV. We did not identify a consistent set of modifiable risk factors associated with vaccine-type HPV after vaccine introduction across the three study waves, underscoring the urgency of vaccination for primary HPV prevention and the limitations of relying on herd protection.