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.
That’s why the CDC’s Advisory Committee on Immunization Practices recommends HPV vaccination for all girls before they become sexually active. But can HPV vaccination help HPV-infected women clear 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.
Future Vaccine Benefit for HPV-Infected Women?
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.”
Bonnez says there is evidence — not proof — that HPV vaccines can prevent future HPV disease in women who have cleared their HPV infections but who still have anti-HPV antibodies in their blood.
Hildesheim says such women may not need vaccination at all.
“Probably a woman who clears infection by herself will be protected from new infection,” he says. “They have proven they can clear the infection without need of a vaccine. So vaccinating these women may not be warranted. But there is not data to prove or disprove this.”
Regardless of whether this is the case, both Hildesheim and Bonnez stress that HPV vaccination is far more effective if given to girls before they become sexually active women.
“This study reinforces the notion that the HPV vaccine should really target women prior to sexual debut,” Hildesheim says. “We know infection happens shortly after sexual initiation. So to vaccinate young women before they initiate sexual activity is the best policy.”
“The biggest bang for the buck is before initiation of sexual activity,” says Bonnez. “That is when the vaccine provides the greatest benefit.”
The Hildesheim study appears in the Aug. 15 issue of the Journal of the American Medical Association.