In women who test positive for human papillomavirus DNA, the bivalent HPV-16/18 vaccination does not induce or accelerate clearance of the infection, according to a phase III study.
Human papillomavirus (HPV) vaccination induces cell-mediated immune responses that are traditionally involved in the eradication of infection, and it has been suggested that the vaccine might benefit women who are already infected, perhaps by enhancing viral clearance. Researchers examined the issue using a cohort drawn from a large, ongoing randomized clinical trial of vaccine efficacy.
The subjects in the main study of vaccine efficacy were nearly 7,500 women aged 18-25 years who resided in Costa Rica, where cervical cancer screening programs incorporate HPV DNA testing along with Pap tests. "Because current management protocols often involve retesting HPV-positive women within months of an initial HPV-positive result before treatment decisions are made, understanding the impact of vaccination on viral clearance in the first 6-12 months following an initial HPV-positive result would be informative," wrote study investigators Dr. Allan Hildesheim of the National Cancer Institute, Rockville, Md., and his associates.
The investigators assessed viral clearance in a subset of 2,055 subjects who were positive for HPV DNA and received either a control immunization or the bivalent HPV-16/18 vaccine that contains viruslike particles only from HPV-16 and HPV-18. This formulation has been approved for use in Australia and is under review for use in the United States and other countries, they noted.
Clearance rates for HPV-16 and/or HPV-18 were not significantly different between the active treatment and placebo treatment groups either 6 months after the initial vaccination was given (33.4% vs. 31.6%) or at 12 months, when the entire series of vaccinations was completed (48.8% vs. 49.8%). In addition, there was no evidence of a vaccine effect in any of several subgroups studied.
The trial was funded by the National Cancer Institute and the National Institutes of Health. Although Dr. Hildesheim reported having no conflicts of interest, other study investigators reported receiving financial support through royalties and employment from GlaxoSmithKline—manufacturer of the vaccine used in the study—and Merck.