Cervical Cancer Vaccines Won't Fight Existing HPV Infection

Study bolsters recommendation that shot be given before onset of sexual activity.

By E.J. Mundell
HealthDay Reporter
Tuesday, August 14, 2007; 12:00 AM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

TUESDAY, Aug. 14 (HealthDay News) -- Cervical cancer vaccines that prevent infection with the human papillomavirus (HPV) do not reduce or eliminate preexisting infections, a new study suggests.

That means that shots such as Gardasil, or a similar, yet-to-be-FDA-approved vaccine, Cervarix, should not be viewed as a treatment for women who've most likely contracted the highly common, sexually transmitted virus through their partners.

"From a public health perspective, a population-wide perspective, the best approach is to vaccinate girls and women before they initiate sexual activity," said study researcher Allan Hildesheim, senior investigator in the division of cancer epidemiology and genetics at the U.S. National Cancer Institute.

"You can then protect individuals prior to their being exposed, since the vaccine doesn't have any effect after infection has happened," he said.

The findings, reported in the Aug. 15 issue of the Journal of the American Medical Association, support a recommendation in June from the U.S. Centers for Disease Control and Prevention that vaccination focus on girls 11 and 12 years of age, most of whom would not have already become sexually active.

Gardasil, which targets four cancer-causing strains of the virus -- 6, 11, 16 and 18 -- should be added to the list of routine school vaccinations, experts say.

On the other hand, "for women who have initiated sexual activity, cervical cancer screening is probably a better preventive measure than vaccination," Hildesheim said.

His team's NCI-funded study, which focused on the Cervarix vaccine, was conducted in Costa Rica and included almost 2,200 women aged 18 to 25. Cervarix has not yet been approved by the U.S. Food and Drug Administration, but its maker, GlaxoSmithKline, has said it believes the shot will gain approval sometime in 2008.

According to Hildesheim, prior studies had already strongly suggested that both Gardasil and Cervarix would be ineffective against preexisting viral infections.

"However, we noticed shortly after the initial licensure of the [Gardasil] vaccine that there was tremendous confusion -- both in the clinical and the lay community, regarding the use of this vaccine among women who were already infected," he said.