Genital human papillomavirus (HPV) is the most common sexually transmitted disease in the United States, and is the cause of virtually all cases of cervical cancer. Although over 100 types of HPV have been identified, two types (HPV-16 and HPV-18) are responsible for nearly 70% of all cervical cancers throughout the world.

A new HPV vaccine, which works by creating antibodies to HPV-16 and HPV-18, as well as two other HPV types, was recently approved by the US Food and Drug Administration (FDA) for females aged 11-26 to prevent infection from HPV. The vaccine, known as Gardasil®, is manufactured by Merck & Co., Inc., and is currently the only HPV vaccine approved by the FDA.

The results of a large clinical phase 3 trial published in the May 10, 2007 issue of the New England Journal of Medicine indicate that this HPV vaccine is highly effective in preventing high-grade cervical lesions, which include precancerous and cancerous lesions.

About the Study

This trial, called Females United to Unilaterally Reduce Endo/Ectocervical Disease (FUTURE) II, was conducted at 90 study sites in 13 countries, and funded by Merck. A total of 12,167 women aged 15-26 participated in the double-blind, placebo-controlled study. Each participant was randomly assigned to receive either the vaccine or a placebo at day 1, month 2, and month 6. After treatment, participants were followed for an average of three years, with visits scheduled for 1 and 6 months after the final injection, and then in months 24, 36, and 48.

The purpose of the trial was to determine whether the HPV vaccine would prevent the development of high-grade cervical lesions, including severe cervical intraepithelial neoplasia (a kind of precancerous cell abnormality indicating the presence of HPV infection), adenocarcinoma in situ, and cervical cancer itself.

For the 10,565 women who had never been exposed to the virus and who received all three vaccines according to protocol, researchers found that the vaccine was highly (98%) effective in preventing high-grade cervical lesions. However, the effectiveness of the vaccine dropped to 44% when the researchers considered all women who were initially enrolled in the study, some of whom did not complete the three-vaccine protocol or were already infected with HPV.

How Does This Affect You?

This study confirms findings from a previous large-scale trial, which found that the HPV vaccine was highly effective in preventing cervical precancers and genital warts.

Overall, both of these large-scale studies seem to indicate that the vaccine can be effective in preventing precancerous and cancerous cervical lesions related to HPV-16 and HPV-18. However, the vaccine can only be expected to work well for women who adhere to the vaccine protocol and have not been previously infected with HPV. This is important, since many women who obtain the vaccine outside of a research study, will not receive all three doses and will already have undiagnosed infection. Furthermore, the vaccine offers no protection for women infected with HPV types other than the four included in the vaccine.

As cervical cancer is one of the most common types of cancer in women, and results in approximately 250,000 deaths worldwide each year, preventive treatment to protect against this disease is highly desirable. However, the vaccine has been the source of controversy among many groups—including policymakers, clinicians, religious groups, and parents—who are divided on when and whether this should be administered to young girls, and whether it should be voluntary or mandatory.

For women who do choose to be immunized with this vaccine, researchers agree that it will be important to continue with other types of cervical cancer screening, such as regular Pap smears. Since this vaccine is new, there are still questions regarding how long the protective effects will last—particularly in women exposed to other types of HPV—and any other adverse effects that may emerge over time. Although the vaccine appears to be safe in the short term for women who are healthy and not pregnant, more research is needed to determine safety and efficacy in women who are pregnant, and women whose immune systems may be compromised.