According to the Centers For Disease Control and Prevention, nearly 20 million people are currently infected with Human Papillomavirus (HPV)—a family of more than 100 common viruses that usually cause harmless skin warts. Certain sexually transmitted strains, however, are now recognized as the major cause of cervical cancer. There is no cure for HPV (though genital warts can be treated in a number of ways) and condoms do not provide complete protection against viruses that may "shed" beyond the protected area. Because of the relative ease of spread, and the strong evidence that cervical cancer is caused by HPV infection, the search has been underway for a vaccine that could prevent the transmission of this virus.

Until now, the only known way to “vaccinate” against cancer was to immunize against Hepatitis B virus, which is strongly linked with liver cancer. A study published in the November 21, 2002 issue of The New England Journal of Medicine details the administration of a vaccine to young women, which was able to significantly reduce the incidence of both HPV-16 infection and, more importantly, the virus’s associated pre-cancerous condition, cervical intraepithelial neoplasia (CIN). In fact, the vaccine demonstrated 100% efficacy. Another study in the same issue suggested that a new vaccine could also be effective against genital herpes in women. This kind of research may represent the dawn of an era in which vaccinations are routinely used to protect against sexually transmitted infections and the diseases they cause.

About the Study

Researchers studied 1533 women between the ages of 16 and 25 to test whether the HPV-16 virus—one of the most common, but not the only, high-risk HPV strains—could be prevented with a vaccine.

Women were enrolled in the study if they were not pregnant, reported no prior abnormal Pap smears, reported no more than 5 male sex partners in their lifetime, and had no detectable HPV-16 DNA in their cervical cells. Other inclusion criteria also applied. At the start of the study, all women received a gynecological exam, which included a Papanicolaou test (Pap smear), external genetical swabs, and cervicovaginal specimens for HPV-16 DNA, which indicates the presence of the virus. Blood samples were also taken to test for levels of HPV-16 antibodies, a measure of the body’s protection against the virus.

The women were randomly assigned to receive either the HPV-16 vaccine or a placebo injection, at the start of the study, and then again after two months and six months (3-dose vaccination). The researchers then followed the women for up to 48 months (average 17.4 months) and periodically collected cervical biopsy specimens and blood samples to detect the presence of CIN, HPV-16 DNA and HPV-16 antibodies. The researchers compared the number of HPV-16 infections and cervical intraepithelial neoplasias in the vaccinated group to the number in the placebo group.

The Findings

All 41 cases of HPV-16 infection occurred in the placebo group meaning the 3-dose HPV-16 vaccine was 100% effective at preventing HPV-16 infection, at least in this population. In addition, all nine cases of HPV-16 related intraepithelial neoplasias occurred among recipients of the placebo injection. The researchers also found an additional 44 cases of cervical intraepithelial neoplasia not associated with HPV-16 infection (22 in both the placebo and vaccine groups). The vaccine was generally well tolerated and there were no serious vaccine-related adverse events; pain at the injection site was the most common event reported for both the vaccine and placebo groups.

Although these results look promising, there are some limitations to the study findings. First, we don’t know the usefulness of this vaccine for older women and women at higher risk for exposure to the HPV viruses—like those who have had more than five sexual partners in a lifetime. Second, this study only focused on the HPV-16 strain, so this vaccine would not affect other cancer-causing strains of HPV. From a public health perspective, a vaccine that prevents infection from a broader spectrum of the HPV strains would be more useful.

Third, though all the cases of HPV-16-related cervical intraepithelial neoplasias occurred in the placebo group, it will only be possible to determine the true effectiveness of the vaccine by administering it to large populations of women, an event that may have to wait for the release of the vaccine to the general public. Finally, even though most women in the study completed the three-dose vaccine regimen, it may be unreasonable to expect the same degree of compliance from the actual population who would most benefit from the vaccine.

How Does This Affect You?

The American Cancer Society estimates that about 13,000 cases of invasive cervical cancer are diagnosed, and more than 4,000 women die each year in the United States. Because at least half of the cases of cervical cancer can be linked to HPV-16 infection, this vaccine could be used for primary cancer prevention—possibly saving thousands of lives. But it may be years before this vaccine has been thoroughly studied and is available for the general public. What can be done in the meantime?

Behaviors such as beginning sexual intercourse at an early age (especially before age 16) and having many sexual partners increase your chances of developing an HPV infection of the cervix. Even after the vaccine is available, there may be other HPV strains and sexually transmitted infections that you could contract, so practicing safe sex or abstinence are still recommended to reduce your risk of exposure. And, don’t forget there already exists an extremely effective method for reducing your risk of cervical cancer from any cause: regular Pap smears.