Cervical Cancer Vaccines Won't Fight Existing HPV Infection

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Other specialists have noticed similar confusion among their peers.

"Each of us has received anecdotal reports of doctors thinking that you can benefit [an infected] woman by vaccinating her," said Dr. Howard Strickler, professor of epidemiology and population health at the Albert Einstein College of Medicine, in New York City. "There are misconceptions in the field," he said.

Even though HPV occurs in a wide variety of strains, Cervarix targets the two strains thought to cause 70 percent of cervical malignancies -- strains 16 and 18.

In the study, the researchers gave the vaccine to about 1,100 young women, all of whom had tested positive for genetic traces of HPV at the beginning of the study. Another group of infected young women received a hepatitis A shot as a "control."

By the end of 12 months, rates of HPV 16 and/or 18 "clearance" -- or absence -- from the body was 48.8 percent in the HPV vaccine group and 49.8 percent among the controls -- a statistical dead heat.

As the experience of the control group showed, the human immune system naturally clears many HPV infections over time. Giving women the vaccine appeared to provide no added benefit, the researchers said.

The investigators also observed no differences between the two groups in terms of the extent of HPV-linked disease, viral antibody load or the results of cervical cell tests conducted in the lab.

"Our results reinforce the notion that this vaccine is meant to protect against infections when they occur, but it isn't effective at helping clear the infection once it has established itself," Hildesheim said.

Still, given the array of HPV viral strains, wouldn't vaccination help protect against viral types a woman had perhaps not yet encountered? Theoretically, that's true, the experts said, and it is for exactly that reason that the CDC recommends the vaccine for women up to age 26.

However, there's currently no test that can determine a woman's HPV history.

"If you are sexually active, there is no way for you to know for sure whether or not you have been exposed to these particular [carcinogenic] strains," explained Hildesheim. They "are very common, and, typically, exposure happens fairly shortly after the initiation of sexual activity," he said. "That's why the best policy is to try and get the vaccine administered prior to sexual debut."