Safety of dose 1 of the nine-valent human papillomavirus vaccine in children aged 4-8 years.

Data on the safety of the nine-valent human papillomavirus (9vHPV) vaccine in children younger than 9 years are limited. We conducted a single-center, open-label descriptive safety study of 150 healthy children aged 4-8 years who received dose 1 of 9vHPV. Active surveillance was performed through structured follow-up assessments, and passive surveillance for serious adverse events was conducted through 11 months post-vaccination. Local reactions were most common (35/150; 23.3%), primarily injection-site pain and tenderness. Systemic events were uncommon and self-limited. Seven hospitalizations (7/150; 4.7%) occurred during follow-up; none were considered related to vaccination or met criteria for unanticipated problems. No vaccine-related serious adverse events were identified. In this descriptive study, dose 1 of 9vHPV was well tolerated in this cohort. Larger studies are needed to further evaluate rare serious adverse events.