Merck's HPV Vaccine Gardasil Produces Immune Response Five Years After Initial Dose

Main Category: Cervical Cancer / HPV Vaccine
Also Included In: Women's Health / Gynecology
Article Date: 28 Jun 2007 - 6:00 PST


Merck's human papillomavirus vaccine Gardasil produces an immune response in women five years after they receive the initial dose of the vaccine, according to a study published on Thursday in the journal Vaccine, Dow Jones reports (Dow Jones, 6/25).

Gardasil in clinical trials has been shown to be 100% effective in preventing infection with HPV strains 16 and 18, which together cause about 70% of cervical cancer cases, and about 99% effective in preventing HPV strains 6 and 11, which together with HPV strains 16 and 18 cause about 90% of genital wart cases, among women not already infected with these strains. FDA in June 2006 approved Gardasil for sale and marketing to girls and women ages nine to 26, and CDC's Advisory Committee on Immunization Practices later that month voted unanimously to recommend that girls ages 11 and 12 receive the vaccine, which is given in a three-shot series. Sanofi Pasteur, a joint company of Merck and Sanofi-Aventis, is funding a campaign advocating for European governments to vaccinate young girls with Gardasil (Kaiser Daily Women's Health Policy Report, 6/22).

For the study, Sven-Eric Olsson of the Karolinska Institutet and colleagues gave 552 women ages 16 to 23 either three doses of Gardasil or a placebo over a six-month period (Olsson et al., Vaccine, 6/21). The participants underwent gynecological examinations, HPV exams and Pap tests during a three-year follow-up period. A subset of 241 women, enrolled in Europe and Brazil, was followed up for five years after receiving the initial dose (Sanofi Pasteur release, 6/21). According to Dow Jones, the women in the subset then were given a "challenge dose" of Gardasil that aimed to simulate exposure to "natural viruses" (Dow Jones, 6/25).

According to the study, antibody levels for HPV declined after the woman received the vaccine but reached a plateau from two years after the initial dose through five years (Vaccine, 6/21). One week after receiving the challenge dose, researchers observed antibody levels that are the same as those observed one month after the completion of the three-dose series. Antibody levels were higher at one month post-challenge than those observed one month after the third dose, according to the study.

"Vaccines that induce long-term protection are usually characterized by the generation of immune memory," the authors write, adding, "The new findings suggest that the efficacy of this vaccine will be long lasting."

Patrick Poirot, vice president of medical and scientific affairs at Sanofi Pasteur, said, "Many health authorities have already recommended human papillomavirus vaccination of girls and young women because maximal benefit is expected when vaccination is completed before exposure to the virus, thus before sexual debut," adding, "The demonstration of immune memory for Gardasil further supports this decision" (Sanofi Pasteur release, 6/21).

"Reprinted with permission from http://www.kaisernetwork.org. You can view the entire Kaiser Daily Health Policy Report, search the archives, or sign up for email delivery at http://www.kaisernetwork.org/dailyreports/healthpolicy. The Kaiser Daily Health Policy Report is published for kaisernetwork.org, a free service of The Henry J. Kaiser Family Foundation . © 2005 Advisory Board Company and Kaiser Family Foundation. All rights reserved.

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