According to the results of a study published in the Journal of the American Medical Association, Cervarix™-a vaccine designed to prevent infection with two high-risk types of human papillomavirus (HPV)-does not treat HPV infections in women who are already infected at the time of vaccination.
Human papillomaviruses (HPV) consist of more than 100 different viruses. Some types of HPV cause warts on the hands or feet; others cause genital warts; and some have been linked with cancer, most notably cervical cancer. The types of HPV most commonly linked with cervical cancer are HPV 16 and HPV 18, but several other high-risk types contribute to cancer as well.
The types of HPV that cause cervical cancer or genital warts are transmitted sexually. HPV infection is extremely common and generally occurs soon after an individual becomes sexually active. Although most infections resolve on their own, some persist and can lead to precancerous or cancerous changes to the cervix, vulva, vagina, penis, and anus.
Vaccines that prevent infection with high-risk types of HPV have the potential to greatly reduce the occurrence of cervical cancer. The HPV vaccine that is currently on the market is Gardasil®, which targets HPV types 6 and 11 (which are linked with genital warts) as well as the cancer-associated types 16 and 18. Another HPV vaccine that may be approved is Cervarix™, which targets HPV types 16 and 18 only. Because HPV types 16 and 18 are thought to account for roughly 70% of all cases of cervical cancer, widespread use of these vaccines would have the potential to eliminate most (but not all) cases of cervical cancer.
Although Cervarix and Gardasil were both developed to prevent infection with high-risk types of HPV-and not to treat existing infections-researchers in Costa Rica evaluated the effect of Cervarix on existing HPV infections.
The study involved 2,189 women between the ages of 18 and 25 years. All women tested positive for HPV prior to vaccination. Half the study participants were vaccinated with Cervarix and half were given a hepatitis A vaccine. The women given the hepatitis A vaccine served as the comparison group.
- By six months, the percent of women who had cleared their HPV infection was 33.4% among women who received Cervarix and 31.6% among women who received the hepatitis A vaccine.
- By 12 months, the percent of women who had cleared their HPV infection was 48.8% among women who received Cervarix and 49.8% among women who received the hepatitis A vaccine.
The researchers conclude that Cervarix does not speed the clearance of existing HPV infections, and should not be used to treat existing HPV infections.
Reference: Hildesheim A, Herrero R, Wacholder S et al. Effect of human papillomavirus 16/18 L1 viruslike particle vaccine among young women with preexisting infection. JAMA. 2007;298:743-753.
Related News:Vaccination Prior to HPV Infection is Key to Protection (05/14/2007)
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