EARLY INITIATION OF THE HPV VACCINE SERIES IN MARYLAND

Abstract

Background: Early initiation (ages 9-10) of the HPV vaccine series increases the likelihood of series completion. Individual- and county-level factors, such as race, ethnicity, income, and degree of urbanicity are associated to vaccine initiation. Thus, we aimed to estimate prevalence and identify county- and individual-level factors associated with initiation of the HPV series, with specific focus on early initiators. Methods: We obtained data for all HPV immunizations administered in Maryland state for 2019-2021, and estimations of total population nine year-olds at the county level for the year 2019. From all potential nine-year-olds living in the state in 2019, we calculated the proportion that had initiated the series by age 11, and that proportion that initiated the series early (ages 9-10). Within each of these two outcomes we calculated prevalence ratios for each of our covariates. Then, among all those that initiated by 11, we ran multilevel log-binomial regression to calculate risk ratios associated to early initiation (as opposed to initiation at 11). Results: Of 74,973 nine-year-olds living in Maryland in 2019, 9,534 (12.7%) had initiated the series by 11, and 1,611 (2.1%) were early initiators. When compared to people of white race, those of African American race were 2.8 times as likely to be early initiators (95% CI 2.5–3.1), and Asians / Pacific Islander were 1.7 times as likely (95% CI 1.4–2.1). When compared to non-Hispanics, Hispanics / Latinos were 1.3 (95% CI 1.3–1.4) times as likely to initiate the series by 11, but were not more likely to be early initiators. Those living in urban areas were more likely to be early initiators (RR 2.1, 95% CI 1.8–2.3), and increasing levels of median household income were associated to lower probabilities of early vaccination (RR of 0.5 [95% CI 0.5–0.6] for quartile 4, when compared to quartile 1). Conclusion: Early initiation of the HPV series is a rare event: only 2% of eligible children started it by age 10. This surveillance data on early initiation describes characteristics of children currently adhering to the recent early-initiation recommendation and suggests areas of opportunities for future interventions