For women already exposed to HPV, shots may not be as helpful


On June 8, the Food and Drug Administration approved the first vaccine to lower a woman’s risk of developing cervical cancer. The vaccine, Gardasil, prevents infection by four strains of human papillomavirus, a common sexually transmitted disease. The vaccine was approved for use in girls and women ages 9 to 26. For women older than 26, Pap smears remain necessary to guard against cervical cancer.

Shari Roan


Three-quarters of all U.S. adults and one-quarter of people ages 15 to 24 have been infected with the human papillomavirus.

In some people, the body clears HPV infection without any consequence. But in some women, the virus causes changes in cells lining the cervix. These abnormal cells can become cancerous. Some 30 strains of HPV exist. The vaccine protects against the two strains that cause 70% of all cervical cancers and two strains that cause genital warts.


Because about half of all U.S. teens have sex before age 18 (6% before age 13), public health officials are encouraging use of the three-shot series at a young age. The national Advisory Committee on Immunization Practices will meet later this month and is expected to recommend routine vaccination for girls ages 11 and 12.

“If you want to vaccinate before exposures occur, then in all reality you want to do it early,” says Dr. Mark Wakabayashi, director of the department of gynecologic oncology at City of Hope. “But then comes the question: When will my daughter become sexually active? And you want to put your head in the sand.”

For sexually active teens and women in their early 20s who may have already been exposed to HPV, it is less clear how the vaccine may be helpful. Studies show that once girls or women become sexually active, they are often rapidly infected with HPV.

Although the vaccine does not cure HPV, it may help people who have one type of HPV from being infected with the other strains. A test can determine whether women are infected with HPV but it does not specify which strains they have. Thus, infected women wouldn’t know whether the vaccine, which protects against strains 16 and 18 (which cause the majority of cervical cancer cases), would still be useful.

The studies on Gardasil were conducted in girls and women ages 9 to 26, so it’s not clear how effective the vaccine would be in conferring immunity in women older than 26.

However, Merck & Co., the maker of Gardasil, is studying the effectiveness of the vaccine in women up to age 45. And GlaxoSmithKline, which is also working on a cervical cancer vaccine, recently announced the results of a study on women ages 26 to 55 showing its vaccine confers immunity against HPV strains 16 and 18.


In the meantime, women should continue to closely follow recommendations for Pap smears, which look for cell changes caused by HPV that, without treatment, can lead to cervical cancer. It’s also likely that even girls who receive Gardasil will eventually need regular Pap smears, says Wakabayashi.

“There are still going to be one-third of the HPV strains out there that will cause cervical cancer” and are not blocked by the vaccine, Wakabayashi says. “We know Pap smears decrease the incidence of cervical cancer.”