Aug. 14, 2007 -- HPV vaccines can't clear the sexually transmitted virus from the bodies of women already infected with cervical-cancer-causing HPV strains.
There are many types of HPV (human papillomavirus). Some types cause cervical cancer, some cause genital warts. Not every infection results in disease, as the immune system usually fights off the virus.
No, shows a U.S./Costa Rica study led by Allan Hildesheim, PhD, a senior investigator at the U.S. National Cancer Institute.
"We found there was no difference in the rate of HPV clearance whether or not women got the vaccine," Hildesheim tells WebMD. "So there is no evidence this vaccine treats established infections."
The FDA has approved Merck's Gardasil HPV vaccine. Gardasil prevents infection from four HPV strains: two linked to cervical cancer and two linked to genital warts. Another HPV vaccine, Cervarix from GlaxoSmithKline, protects against the same two cancer-linked HPV strains. Cervarix is approved in Australia; U.S. approval is expected next year.
While the Hildesheim study is testing Cervarix, Hildesheim says Gardasil studies have also shown that the vaccine cannot speed viral clearance in women who already have HPV infection.
It is not yet known whether vaccination of already-infected women can prevent future HPV infections.
Viral clearance means that researchers can no longer detect viral DNA in a person's blood. It may not mean that the virus is completely eliminated from the body, says William Bonnez, MD, associate professor of medicine at the University of Rochester, N.Y. Bonnez, one of the inventors of HPV vaccines, receives royalties from both GlaxoSmithKline and Merck. He was not involved in the Hildesheim study.
"HPV vaccination does not affect present HPV infection, but it may prevent future HPV infections and diseases, regardless of what the present [infection] status is," Bonnez tells WebMD. "In other words, you do not vaccinate for the present, but you do it for the future."