Abstract
BACKGROUND: The Costa Rica HPV Vaccine Trial provided initial evidence that 1 dose of the bivalent human papillomavirus (HPV) vaccine induces stabilizing antibody levels that may provide extended protection against HPV-16/18 infections. We report antibody seropositivity and stability 11 to 16 years after vaccination. METHODS: We invited a random subset of Costa Rica HPV Vaccine Trial participants (n = 398) who had received 3 doses and all women (n = 203) who had received 1 dose at 18 to 25 years of age to follow-up visits 11, 14, and 16 years after vaccination. We calculated HPV-16 and HPV-18 seropositivity and assessed change in enzyme-linked immunosorbent assay antibody levels 11 to 16 years after vaccination among 500 participants. RESULTS: By year 16, 99.4% (95% confidence interval [CI] = 96.8% to 100.0%) and 100.0% (95% CI = 98.9% to 100.0%) of 1-dose and 3-dose recipients, respectively, were HPV-16 seropositive and 98.8% (95% CI = 95.9% to 99.9%) and 100% (95% CI = 98.9% to 100.0%) of 1-dose and 3-dose recipients, respectively, were HPV-18 seropositive. Between years 11 and 16, women who had received 3 doses had a small but statistically significant decrease in the geometric mean concentration for HPV-16 of ‒12.4% (95% CI = ‒16.3% to ‒8.4%) and HPV-18 of ‒13.4% (95% CI = ‒17.2% to ‒9.4%). Among women who had received 1 dose, the decrease was statistically significant for HPV-16 at ‒8.9 (95% CI = ‒14.2% to ‒3.1%) but nonsignificant for HPV-18. Geometric mean concentration ratios of 3:1 dose (year 16) were 3.0 and 2.2 for HPV-16 and HPV-18, respectively. CONCLUSIONS: HPV-16/18 seropositivity remained exceedingly high 16 years after vaccination. Over 5 years, small declines in antibodies were observed. Women should have protection for at least 20 years and likely much longer at the observed rate of decline.