Abstract
BACKGROUND: To assess the enduring protective efficacy of the recombinant human papilloma virus (HPV) 16/18 bivalent vaccine (produced in Escherichia coli) in preventing HPV infection. METHODS: A long-term follow-up study was conducted in Xinmi, Henan Province, in September 2022, 9 years post-administration of the initial vaccine dose. This study was grounded in the phase III clinical trial of the vaccine (NCT01735006). Participants were recalled to collect exfoliated cervical cells for HPV DNA genotyping. The long-term protective efficacy of the vaccine against HPV infection was evaluated using Poisson distribution. RESULTS: A total of 1 123 volunteers were recalled, comprising 558 individuals in the experimental group and 565 in the control group, with mean ages of 30.80 ± 7.33 years and 30.64 ± 7.51 years, respectively. At baseline (0 days before vaccination), 147 participants (13.09%) were infected with any type of HPV. By the ninth year of follow-up, the overall HPV infection rate within the entire cohort had increased to 16.65%. In the intention-to-treat analysis, the demonstrated protective efficacy against HPV-16, HPV-18, and HPV-16/18 was 83.12% (95% confidence interval [CI]: 24.20-98.17), 100.00% (95% CI: -10.50 to 100.00) and 87.34% (95% CI: 46.17-98.59), respectively. In the modified intention-to-treat analysis, the protective efficacy of the vaccine against HPV-16, HPV-18, and HPV-16/18 was 82.90% (95% CI: 23.20-98.14), 100.00% (-10.71 to 100.00), and 87.36% (95% CI: 46.20-98.59), respectively. CONCLUSIONS: Vaccination with the bivalent HPV vaccine offers long-term protection against HPV-16/18 infections for at least 9 years.