Pediatric practices that introduced HPV vaccine at ages 9-10 instead of 11-12 had higher rates of series initiation and completion by age 13, according to results of a cluster randomized trial presented at IDWeek 2026.
Sean T. O'Leary, MD, MPH, of the University of Colorado School of Medicine and Children's Hospital Colorado, who presented the data, explained that the CDC's Advisory Committee on Immunization Practices recommends routine HPV vaccination at age 11 or 12, and the series can begin at 9. The American Academy of Pediatrics recommends starting the series between ages 9 and 12, at an age the clinician considers best for acceptance and completion.
Observational studies suggest increased uptake of the HPV vaccine when the series is introduced earlier, but their limitations preclude a cause-and-effect conclusion.
Methodology
The trial enrolled 31 pediatric practices in Colorado and California that were initiating HPV vaccination at 11-12. Using covariate-constrained randomization to balance the arms on the number of patients ages 9-13, baseline completion rates at age 13 and Medicaid share, investigators assigned 16 practices (106 clinicians) to introduce the vaccine at 9-10 and 15 practices (112 clinicians) to continue at 11-12.
Clinicians in both arms received an online training module on recommending the HPV vaccine and on practice-based strategies to improve vaccination. They also took part in annual Zoom calls with feedback on missed HPV vaccination opportunities. The 9-10 arm additionally received guidance on how to word the recommendation to parents at that age.
The primary outcome was median age at series completion. Secondary outcomes were median age at initiation and the proportions initiating and completing by age 13. Investigators analyzed the data with Cox proportional hazards models adjusted for clustering within practices, patient age, gender, state and the randomization balancing factors.
Baseline Characteristics
The analysis included 62,246 children who were between ages 9.0 and 10.5 at some point during the study period (28,407 in the 9-10 arm and 33,839 in the 11-12 arm). Baseline age was 8.1 years in both arms. At baseline, up-to-date rates among 9- to 13-year-olds were 28.8% in the 9-10 arm and 27.8% in the 11-12 arm. Medicaid share was 22% and 23%, respectively. Practices in the 9-10 arm were smaller, averaging 1,689 patients ages 9-13 and 5.4 full-time-equivalent providers, versus 2,020 patients and 7.6 providers in the 11-12 arm.
Key Findings
Median age at initiation was 11.0 years in the 9-10 arm and 11.8 years in the 11-12 arm (difference, -0.8 years; 95% CI, -1.3 to -0.1). Median age at completion was 12.2 and 13.3 years, respectively (difference, -1.1 years; 95% CI, -1.9 to -0.3).
By age 13, 77.2% of adolescents in the 9-10 arm and 67.0% in the 11-12 arm initiated the vaccination series. Completion by age 13 was 61.7% versus 45.1%, respectively. The adjusted hazard ratio for 9-10 versus 11-12 was 2.19 (95% CI, 1.84-2.62; P<.001) for initiation and 2.37 (95% CI, 1.94-2.89; P<.001) for completion.
Differences at age 13 varied by state. In Colorado, the gap between the 9-10 and 11-12 arms was 6.9 percentage points for initiation and 12.2 points for completion. In California, it was 16.7 and 25.6 points, respectively.
The investigators looked for negative effects of the earlier schedule on care delivery. The proportion of children with well-child visits at ages 11-12 did not differ between arms, nor did the proportion up to date for meningococcal and Tdap vaccines by age 13.
Parent and Clinician Perceptions
Interviews with 18 clinicians and 17 office staff in the 9-10 arm showed that many parents were perceived as receptive to vaccination at 9-10. When pushback occurred, it often stemmed from an expectation of a visit without shots. Clinicians reported that discussions appeared shorter and sexual activity was less prominent in the discussion.
Clinician surveys at 1, 6, 12, 16, 24, 30 and 36 months showed that almost all clinicians in the 9-10 arm switched quickly from 11-12 to 9-10. Parental concerns, questions, pushback, hesitancy and adherence did not differ between arms, and clinicians in both arms reported similar perceived ability to convince parents. Discussion times were shorter in the 9-10 arm. The qualitative and survey findings were published in Pediatrics.
Limitations include the study's setting in two states, the urban and suburban nature of the practices, which may limit applicability to rural areas, and the inability to account for adolescents who left the practices.
The study was supported by a National Cancer Institute-funded grant.
