Teenagers had better vaccine coverage against human papillomavirus (HPV) if they were vaccinated at earlier ages as older children instead of early adolescents, a retrospective study showed.

Early initiators vaccinated at age 9 or 10 were, compared with those who initiated at ages 11 to 12, more likely to complete the HPV vaccine series by age 13 (74.0% vs 31.3%) and age 15 (91.7% vs 82.7%), two findings that persisted in multivariate analysis, reported Elizabeth Goodman, MD, MBA, and fellow employees of Merck in North Wales, Pennsylvania.

As for the question of whether early initiation might improve series completion by shifting the first dose to the late childhood developmental stage, early HPV vaccine initiation was associated with a numerically lower likelihood of completion within 3 years (82.3% vs. 84.9%) that did not reach statistical significance upon multivariable adjustment, Goodman and colleagues reported in Pediatrics.

“These findings suggest that, by increasing the available time between initiation and target completion age, early initiation gives providers more touch points and therefore more opportunities to complete the series. The idea that early initiation could increase completion because the vaccine was given at an earlier developmental period was not supported, nor do our findings suggest that early initiation alters disparities in HPV series completion,” according to the investigators.

Moving routine HPV vaccination from ages 11 to 12 years — the current Advisory Committee on Immunization Practices-recommended age — to ages 9 to 10 may improve coverage rates in early- and mid-adolescence, “thereby increasing the public health benefit of vaccination,” the Merck group suggested.

“To date, no study with national scope has assessed if earlier initiation is associated with improved HPV vaccination series completion nor explored mechanisms underlying such an association,” Goodman and colleagues wrote. “Understanding the pathways through which early initiation functions could help optimize series completion in early and mid-adolescence, when completion before sexual debut is more likely and maximum public health benefits would accrue.”

HPV is the most common sexually transmitted infection globally that contributes to hundreds of thousands of new cancer cases and deaths annually in the U.S. HPV immunization is most effective if given before sexual debut, study authors noted.

To complete the study, Goodman and colleagues reported using data from the National Immunization Survey (NIS)-Teen, 2017-2020, from which a retrospective cohort of nearly 20,000 15- to 17-year-olds who initiated HPV vaccination between ages 9 and 12 was assembled. The research team then examined series completion by ages 13 and 15.

Logistic regression modeling did not suggest that early initiation altered sociodemographic, geographic, or provider-based disparities in series completion, the authors reported.

One limitation of the study was that the research team assigned birth cohorts based on age at interview and survey year because date of birth was not available in public-use data, Goodman and colleagues noted. However, they said that any misclassification was distributed across all birth cohorts and likely to have minimal impact on overall findings.

Although the study was national in scope, it should not be considered nationally representative, Goodman and colleagues further cautioned. For instance, report of vaccination status relied on parental consent to contact providers, who were the ones responding to the NIS-Teen questionnaire.

“Future research on acceptability of and barriers to routine vaccination at ages 9 to 10 years could promote uptake and completion before sexual debut,” Goodman and colleagues concluded, “thereby maximizing HPV vaccine effectiveness.”

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