HPV Vaccine Won't Treat Pre-existing Infection

ROCKVILLE, Md., Aug. 14 -- The bivalent vaccine that protects against infection with human papillomavirus does not affect HPV clearance in women with pre-existing infections and should not be considered a treatment modality.

There was no evidence of viral clearance at 6 or 12 months in the 1,088 women with existing HPV infection who received the bivalent HPV-16/18 vaccine, when compared with controls, according to a study reported in the Aug. 15, 2007 issue of the Journal of The American Medical Association.

At six months, the clearance rates for HPV-16/18 were 33.4% among women who received the HPV vaccine and 31.6% among women in the control group, said researchers led by Allan Hildesheim, Ph.D., of the National Cancer Institutes. At one year, the clearance rates were 48.8% in the HPV vaccine group, compared with 49.8% in the control group.

Vaccine efficacy for preventing persistent infection with HPV-16, HPV-18 or both was 2.5% (95% CI, -9.8% to 13.5%) at six months and -2.0% (95% CI, -24.3% to 16.3%) at one year, the researchers said.

Noting that some women may be interested in the HPV vaccine to treat existing infections, the researchers concluded that their results "demonstrate that in women positive for HPV DNA, HPV-16/18 vaccination does not accelerate clearance of the virus and should not be used for purposes of treating prevalent infections."

The phase 3 trial took place in two provinces of Costa Rica and comprised a total of 2,189 women ages 18 to 25 who were positive for HPV DNA at the time of enrollment. The women were followed for at least 6 months and the number found to have HPV DNA upon follow-up examination was determined. The new study used the bivalent HPV-16/18 vaccine (Cervarix), one of two available. The trial is ongoing. Its main analysis will focus on the prophylactic effects of the vaccine.

There was no evidence that HPV vaccination altered rates of viral clearance when the cohort was stratified by entry characteristics reflective of disease extent including HPV-16/18 antibody results, cytologic results and HPV viral load, the researchers said.

Moreover, there was also no evidence of therapeutic effects among sub-group analyses based on other parameters thought to influence clearance rate and vaccine efficacy including time since first sexual activity, use of birth control pills, smoking, and infection with C. trachomatis or B. gonorrhoeae.

When researchers analyzed the vaccine's efficacy by specific, single HPV type, they found that the viral clearance was 27.3% and 27.5% for HPV-16 at six months for the cases and controls, respectively. Six month viral clearance rates for HPV-18 were 46.1% for women who received the HPV vaccine and 44.7% among those who received the control vaccine.

At 12 months, the viral clearance for HPV-16 was 43.9% among women who received the HPV vaccine compared with 45.9% among controls. The viral clearance for HPV-18 was 59.3% in the HPV vaccinated group and 60.7% among controls at 12 months.

The new findings reinforce that women with abnormal pap smears results or positive HPV DNA should be treated in accordance with current guidelines, not with the vaccine, pointed out Laurie E. Markowitz, M.D., of the CDC in Atlanta, in an accompanying editorial.

Previous research has also shown a lack of therapeutic efficacy with the quadrivalent HPV vaccine (Gardasil), she noted.

"These data, along with data demonstrating the high likelihood of acquiring HPV infection soon after onset of sexual activity and data on sexual behavior in the United States, all contributed to recommendations for routine immunization at 11 to 12 years of age," she wrote. "Because the vaccine has no therapeutic efficacy, the greatest effect will be realized if the vaccine is administered before sexual debut, prior to exposure to HPV."

Going forward, data on longer-term safety and immunogenicity as well as post licensure safety monitoring will be crucial especially since this vaccination program is targeting 11- to 12-year-olds.

The trial is sponsored and funded by a grant from the National Cancer Institute, with support from the National Institutes of Health Office for Research on Women's Health and support from the Ministry of Health of Costa Rica. Vaccine was provided by GSK Biologicals.