Recent guidelines from the American Cancer Society stress HPV vaccination series initiation at the youngest opportunity, i.e., age 9 years. There are limited data on the association between initiating HPV vaccination at ages 9-10 years and up-to-date (UTD) status. In this study, we compare nationally representative UTD HPV vaccination rates between adolescents who initiated the series younger (ages 9-10 years) vs. older (≥ age 11 years). Five years of pooled data (2016-2020) from National Immunization Survey-Teen were used to estimate the UTD HPV vaccination prevalence among younger vs. older initiating 13-17-year-olds. Adjusted logistic regression models estimated prevalence ratios (aPRs), differences (aDs), and difference in differences (aDDs) in prevalence of being UTD to assess the overall association of age at initiation with being UTD and differences in sociodemographic predictors of being UTD among younger vs. older initiators. UTD prevalence for younger initiators was 93% compared with 72% among older initiators (aPR: 1.27,95%CI: 1.24,1.31). Among older initiators, UTD prevalence was significantly different by sex, insurance status, and current age; no such differences were observed among younger initiators. Results indicate that younger initiation is associated with a 27% higher UTD prevalence, highlighting the importance of promoting younger initiation, particularly among those with health-care barriers.
Keywords: HPV vaccination; NIS-Teen; cancer prevention; public health; younger initiation.