The human papilloma virus (HPV) vaccine prevents infection with certain species of human papillomavirus associated with the development of cervical cancer, genital warts, and some less common cancers. Two HPV vaccines are currently on the market: Gardasil and Cervarix.
Both vaccines protect against the two HPV types (HPV-16 and HPV-18) that cause 70% of cervical cancers, 80% of anal cancers, 60% of vaginal cancers, and 40% of vulvar cancers. These HPV types also cause most HPV induced oral cancers, and some other rare genital cancers. Gardasil also protects against the two HPV types (HPV-6 and HPV-11) that cause 90% of genital warts.
Both vaccines have been shown to prevent potentially precancerous lesions of the cervix. Gardasil has been shown to prevent potential precursors to anal, vulvar, vaginal, and penile cancers. HPV vaccines are expected to protect against HPV induced cancers of these areas as well as HPV induced oral cancers.
The World Health Organization (WHO), as well as public health officials in Australia, Canada, Europe, and the United States recommend vaccination of young women against HPV to prevent cervical cancer, and to reduce the number of treatments for cervical cancer precursors.
Worldwide, HPV is the most common sexually transmitted infection in adults. For example, more than 80% of American women will have contracted at least one strain of HPV by age fifty.
Although most women infected with genital HPV will not have complications from the virus, worldwide there are an estimated 529,000 new cases of cervical cancer and 275,000 deaths per year. About 85 percent of cancers, and eighty percent of deaths from cervical cancer occur in developing countries. In the United States, most of the approximately 11,000 cervical cancers found annually occur in women who have never had a Pap smear, or not had one in the previous five years. HPV is also the cause of cervical intraepithelial neoplasia (CIN). CIN is a precursor to cervical cancer, and is painful and costly to treat. It is not known how many women worldwide are diagnosed with CIN.
Since the vaccine only covers some high-risk types of HPV, experts still recommend that women get regular Pap smear screening even after vaccination.
HPV vaccination is approved for use in males in many areas. In addition to protecting their partners from cervical cancer, vaccination can protect males against anal cancer, and may prevent other HPV associated cancers. Gardasil can also protect males against genital warts. HPV vaccination has been recommended for males in the United States, where vaccine uptake among women has been low. Vaccination is also recommended in populations at higher risk for HPV associated cancers, such as men who have sex with men and those with compromised immune response.
Both Gardasil and Cervarix have been shown to prevent cervical dysplasia from the high-risk HPV types 16 and 18 and some protection against a few closely related high-risk HPV types. However, there are other high-risk HPV types that are not affected by the vaccines. The protection against HPV 16 and 18 has lasted 5 years after vaccination for Gardasil and more than 6 years for Cervarix. It is thought that booster vaccines will not be necessary.
Gardasil also protects against low-risk HPV types 6 and 11, which do not cause cancer, but do cause genital warts.
A recent analysis of data from a clinical trial of Cervarix found that this vaccine is just as effective at protecting women against persistent HPV 16 and 18 infection in the anus as it is at protecting them from these infections in the cervix. Overall, about 30 percent of cervical cancers will not be prevented by these vaccines. Also, in the case of Gardasil, 10 percent of genital warts will not be prevented by the vaccine. Neither vaccine prevents other sexually transmitted diseases, nor do they treat HPV infection or cervical cancer.
HPV types 16, 18 and 45 contribute to 94% of cervical adenocarcinoma (cancers originating in the glandular cells of the cervix). While most cervical cancer arises in the squamous cells, adenocarcinomas make up a sizable minority of cancers. Further, Pap smears are not as effective at detecting adenocarcinomas, so where Pap screening programs are in place, a larger proportion of the remaining cancers are adenocarcinomas.Trials suggest that HPV vaccines may also reduce the incidence of adenocarcinoma.