HPV vaccine reduces risk for strains not in shot

The quadrivalent human papillomavirus vaccine, Gardasil, appears to defend against viral types not included in it. This finding is especially true for women not exposed to the virus before vaccination, according to a pair of papers published in the April 1 Journal of Infectious Diseases.

"We have to immunize young women and young girls before they become sexually active. That's when the benefit will occur," said Darron R. Brown, MD, a professor of medicine, microbiology and immunology at Indiana University School of Medicine in Indianapolis.

Researchers analyzed data on 17,622 women age 16 to 26 who were taking part in phase III efficacy studies set up by Merck Research Laboratories, the vaccine's manufacturer. One paper found the preventive reduced by 32.5% the risk of precancerous changes in cervical cell growth caused by 10 viral types not included in the vaccine in women who were uninfected when they received the shot. More details are online (link).

The second study documented that when both HPV-naïve and those already exposed to this virus were grouped together, the risk was cut by 15.1%. The paper also is available online (link).

"It's not completely understood why," said Dr. Brown, the lead author on the first paper and a co-author on the second. "There are families of related HPV types, and we think the antibodies made when women are vaccinated have an effect against other closely related viral types."

Experts say questions about the duration of immunity, particularly among those who do not receive all three shots in the series, need to be answered to determine the vaccine's true population impact. Also, although the protection against non-included strains was statistically significant, it was not completely additive and only provided some defense against these pathogens.

Public health agencies and medical societies have been working to increase the vaccine's uptake since the Food and Drug Administration approved it June 8, 2006. The American Medical Association supports its use along with routine cervical cancer screening in the context of adolescent and young adult health care visits. Students and parents also should be educated about HPV and the availability of the preventive.