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.
Published by Oxford University Press 2024.