Aug. 14, 2007 -- HPV vaccines can't clear the sexually transmitted virus
from the bodies of women already infected with cervical-cancer-causing HPV
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
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.
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
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
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.
SOURCES: Hildesheim, A. TheJournal of the American Medical
Association, Aug. 15, 2007; vol 298: pp 743-753. Markowitz, L.E.
TheJournal of the American Medical Association, Aug. 15, 2007; vol 298:
pp 805-806. CDC: Advisory Committee on Immunization Practices, record of the
proceedings, Feb. 21-22, 2007. Allan Hildesheim, PhD, senior investigator,
division of cancer epidemiology and genetics, National Cancer Institute, NIH,
Bethesda, Md. William Bonnez, MD, associate professor of medicine, University
of Rochester, N.Y.