State and territory immunization program activities and their association with human papillomavirus vaccine initiation in the United States of America: A multilevel approach

This study evaluates the association between immunization program (IP) activities aimed at increasing HPV vaccination among adolescents and their impact on initiation rates. Our data sources are: (i) 2016 AIM Annual Survey and (ii) 2019 National Immunization Survey-Teen. We estimated the prevalence of HPV vaccine initiation using a multilevel Poisson model, combining state-level IP data and individual characteristics of adolescents. We calculated the prevalence ratio (PR) of HPV initiation among adolescents to compare the effects of IP activities, adjusting for state of residence, age, sex, maternal education, and ethnicity. A total of 17,390 teens aged 13 and 17 were evaluated. States with publicly available school-based adolescent coverage rates and/or exemptions (PRw, activity Dadjusted: 1.08, 95% CI: 1.02, 1.14), and those that expanded the number of pharmacies entering HPV vaccination data (PRw, activity Nadjusted; 1.06, 95% CI: 1.02, 1.10) in Immunization Information Systems (IIS), had higher HPV vaccine initiation rates compared to states that did not implement these strategies. When stratifying, these findings were present in the younger group (13-15 years, PRw, activity D adjusted: 1.10, 95% CI: 1.01, 1.18; PRw. activity N adjusted: 1.10, 95% CI: 1.05, 1.16), but not in the older group (16-17 years, PRw, activity D adjusted: 1.05, 95% CI: 0.95, 1.15; PRw. activity N adjusted: 1.00, 95% CI: 0.94, 1.06). States that expanded the number of school-located programs entering HPV vaccine records in IIS (PRw, activity Eadjusted: 1.08, 95% CI: 1.01, 1.15) had higher vaccine initiation prevalence in the younger group but not in the older group. Limitations include a lack of operational definitions for IP activities, potential biases in the NIS-Teen survey, and reliance on provider-reported HPV vaccination. Nonetheless, these results highlight immunization activities that support national efforts to increase HPV vaccine uptake and inform public health programs on effective HPV vaccine promotion.