HPV antibody concentrations among male and female adolescents after single-dose 9-valent HPV vaccination.

BACKGROUND: Efficacy and immunogenicity of single-dose human papillomavirus (HPV) vaccination have been demonstrated among females; less is known about single-dose vaccination among males. We assessed sex differences in antibody response 12-48 months post-vaccination among adolescents who received a single 9-valent HPV vaccine (9vHPV) dose. METHODS: Participants were recruited from an integrated healthcare delivery system in Oregon and southwest Washington. Adolescents who received a single 9vHPV dose at ages 9-12 years, 12-48 months prior to study enrollment, were identified. Serum antibody testing for each 9vHPV type (HPV6, 11, 16, 18, 31, 33, 45, 52, 58) was conducted using M9ELISA. We compared antibody detection and geometric mean antibody concentrations (GMCs) among males to females. RESULTS: Among 111 male and 96 female participants, age at vaccination (>95% at ages 11 or 12 years) and time since vaccination (median: 20 months) were similar by sex. Among males and females, 80.2% and 89.6% had detectable antibodies for all types, with no significant sex difference. Type-specific detection ranged from 84.7% to 99.1% for males and 91.7% to 99.0% for females, with no significant sex differences. GMCs were 31-50% lower among males than females for all types (range of GMC ratios adjusted for time since vaccination: 0.50-0.69). CONCLUSIONS: One to four years after single-dose 9vHPV vaccination, males had similar detection but lower antibody concentrations than females. Because very low levels of antibody are thought to protect against HPV, the clinical significance of these sex differences is unknown.