Background: The 9-valent HPV (9vHPV) vaccine was developed to prevent infection and disease related to 9 HPV types (HPV6/11/16/18/31/33/45/52/58) which cause approximately 90% of cervical cancers, HPV-related vulvar, vaginal and anal cancers, and genital warts worldwide. In a pivotal efficacy study, the 9vHPV vaccine prevented infection and disease due to the 9 vaccine types. Duration of protection remains to be determined. Vaccines that induce long-term protection are generally characterized by the generation of immune memory. The purpose of this report is to assess the persistence of HPV antibody response and existence of immune memory at 5years post-vaccination.
Methods: A subset of subjects (N=150) who received 3 doses of 9vHPV vaccine at day 1, month 2 and month 6 in the pivotal efficacy study continued in a study extension and received a fourth dose of 9vHPV vaccine at month 60. Serum HPV antibody levels were measured pre-dose 4 and at 7 and 28days post-dose 4 by competitive Luminex immunoassay. Adverse events were assessed using a vaccination report card.
Results: HPV antibodies induced following the 3-dose series of 9vHPV vaccine in the base study persisted through month 60 with seropositivity rates ranging from 77.5% to 100%. Geometric mean titers at 1week and 1month post-dose 4 were 1.25-4.10 and 1.65-4.88-fold higher, respectively, than levels observed 1month following the completion of the three-dose primary series. Seropositivity rates were >99% and 100% at 1week and 1month post-dose 4, respectively. The fourth dose of 9vHPV vaccine was generally well tolerated.
Conclusions: A three-dose regimen of the 9vHPV vaccine induced persistent HPV antibody response through 5years post-vaccination. Administration of a fourth dose resulted in a strong anamnestic response to all 9 vaccine types. These findings suggest that the efficacy of the 9vHPV vaccine will be long lasting. Clinical Trials.gov Identifier:NCT00543543.
Keywords: 9vHPV vaccine; Clinical trial; Human papillomavirus; Immune memory; Immunogenicity.
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