Most cervical cancers are caused by infection with the human papillomavirus (HPV). HPV is the most common sexually transmitted infection in the United States. Although many women infected with the virus eventually clear the infection, some women develop a persistent (lasting) infection, which is a risk factor for cervical cancer. The recent news about Gardasil, a new HPV vaccine, has prompted many questions about the use and effectiveness of this vaccine. To help answer common questions about the vaccine, Cancer.Net discussed the HPV vaccine with Maurie Markman, MD.

Q. What is the purpose of the HPV vaccine, and who needs to be vaccinated?

A. The goal of this vaccination is to prevent the establishment of a persistent HPV infection after a person has been exposed to the virus through sexual contact. Strong scientific evidence demonstrates that a persistent HPV infection is required for cervical cancer to begin developing.

The U.S. Food and Drug Administration (FDA) has approved Gardasil for use in girls and women between the ages of nine and 26. The vaccine is approved to prevent disease associated with HPV infection from specific viral subtypes known to cause genital warts and precancerous cervical lesions (areas of abnormal tissue), as well as cervical cancer.

Q. How effective is the vaccine?

A. Several large clinical trials have revealed that the vaccine is highly effective in preventing precancerous cervical lesions, assuming a woman does not have a preexisting (before vaccination) persistent HPV infection. Because it takes many years before a precancerous lesion develops into an invasive cancer, it will likely take at least a decade before there will be evidence that the number of new cases of cervical cancer in vaccinated individuals has been reduced. However, in view of the known very strong association between persistent HPV infection, the development of precancerous cervical lesions, and cancer of the cervix, it is essentially certain a substantial reduction in the risk of cervical cancer will be clearly seen with sufficient time for follow-up.

Q. Does the vaccine work right away? How long does it last?

A. The vaccine appears to be very effective in preventing persistent HPV infection, as long as there is no preexisting infection with the virus. It is important to note that the vaccine will not eliminate an existing persistent HPV infection.

It is currently unknown how long a single series of vaccinations with the HPV vaccine will last, and if revaccination will be required, and how often. Existing data suggest that immunity against the development of an infection upon exposure to the virus will last a minimum of three to five years, and perhaps much longer. Further follow-up of people who received the vaccine in clinical trials will provide important information regarding if, and when, the necessary degree of immunity decreases to a point where re-immunization is required.

Q. How does this vaccine affect a woman’s need for a regular Pap test?

A. There have been no specific recommendations for how HPV vaccination should influence existing, well-established guidelines for regular Pap tests. For now, it is strongly recommended that current guidelines should be followed. This important issue will be directly addressed in the future by experts in this area.

Q. What are the most important things a patient should know about the HPV vaccine?

A. Existing data indicate HPV vaccination is both safe and highly effective in preventing persistent infection by a virus known to be the cause of cervical cancer. It is extremely important that patients understand this vaccine works to prevent a persistent HPV infection, but it is not an effective treatment to eliminate such an infection once it is established.

Dr. Markman is Vice President for Clinical Research, Professor of Cancer Medicine and Chair ad interim, Department of Gynecologic Medical Oncology at The University of Texas M.D. Anderson Cancer Center in Houston. He serves as the Cancer.Net Associate Editor for gynecologic cancers.