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HPV vaccine protects beyond six years

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Women vaccinated with bivalent human papillomavirus vaccine experienced sustained protection against precancerous cervical lesions caused by vaccine types 16 and 18 up to 6.4 years after first vaccination, final analyses from a long-term follow-up trial indicated.

“So far, our study shows the longest duration of protection against HPV 16 and HPV 18 infections for a licensed prophylactic HPV vaccine,” researchers from the HPV-007 Study Group wrote. Previous trials have established protection up to five years with the quadrivalent HPV vaccine (Gardasil, Merck).

The follow up study included HPV-naïve women aged 15 to 25 years from 27 sites in three countries,393 of whom were in the vaccine group and 383 from the placebo group.

Data indicated that the bivalent vaccine (Cervarix, GlaxoSmithKline) was 100% effective at preventing cervical intraepithelial neoplasia grade 1 and above associated with the two vaccine types, and 71.9% effective against all lesions, regardless of HPV type. Vaccine efficacy was 95.3% for preventing infections caused by these two types throughout the follow-up period, and antibody concentrations were 12-fold higher among women who received the vaccine compared to women who experienced natural infection.

Participants in the placebo group continued to experience cases of cervical intraepithelial neoplasia throughout the study, indicating the vaccine was effective during continuous exposure.

The trial findings provided additional indirect evidence that the bivalent vaccine may confer protection beyond the HPV types included in the vaccine, according to the researchers. Vaccine recipients also had a lower incidence of infection with HPV 31 compared with those in the placebo group (13 vs. 30), and a similar lower incidence of HPV 45 (5 vs. 20).

“HPV 31 and HPV 45 are among the types most frequently associated with cervical cancer after HPV 16 and HPV 18, and are responsible for 10% of all cervical cancer cases,” the researchers wrote.

Further follow-up studies are planned in a subset of patients to determine vaccine efficacy at 9.5 years. Determining the vaccine’s duration of protection is a priority because the incidence of cervical cancer peaks long after girls become sexually active, an average of 30 years after adolescence, according to the researchers.

In a comment accompanying the study, Gary M. Clifford, MD, of the International Agency for Research on Cancer in Lyon, France offered his thoughts on vaccine timing. “The target age, thus, is a balance being early enough to catch girls before sexual debut, but late enough to provide an as yet unknown duration of immunity that protects during as many subsequent years of sexual activity as possible.”

The GlaxoSmithKlineVaccine HPV-007 Study Group. Lancet. 2009;DOI:10.1016/S0140-6736(09)61567-1.