CHICAGO An aggressive strategy of vaccinating older women against cervical cancer could deliver a crippling blow against the disease, cutting rates for that type of cancer in half for women through age 45, U.S. researchers said on Saturday.
Using a mathematical model, they showed that vaccinating women in the United States by ages 12 through 45 against the cancer-causing human papillomavirus, or HPV, could reduce cases of cervical cancer by 85 percent for 12-year-olds and up to 55 percent for 45-year-old women.
It could lower rates by 34 to 67 percent for 25-year-old women, Warner Huh of the University of Alabama told a meeting in Washington of the American Society for Microbiology and the Infectious Diseases Society of America.
The model assumed 100 percent vaccination rates, which would be difficult to achieve in the United States.
Most cases of cervical cancer are caused by the sexually transmitted human papilloma virus.
Merck and Co's Gardasil vaccine is designed to protect against HPV types 16 and 18, which are known to cause about 70 percent of all cases of cervical cancer. It also is designed to protect against HPV strains 6 and 11, which cause genital warts.
Gardasil is approved in the United States for use in girls and women ages 9 to 26, but Merck is seeking to expand its use to older women. The thinking has been that girls must be vaccinated before they are sexually active, because HPV is so common.
The vaccine does not protect anyone who has already been infected with one of the strains of HPV.
Huh's calculations included clinical trial data on GlaxoSmithKline's Cervarix vaccine, which is not yet approved for sale in the United States but which is approved in Europe.
He assumed Cervarix gave 95 percent protection against HPV types 16 and 18, and 27 percent efficacy against all other high-risk HPV types.
Vaccinating women over age 26 has not been approved by the U.S. Food and Drug Administration and is not included in U.S. Centers for Disease Control and Prevention guidelines.
An estimated 11,070 new cases of cervical cancer will be diagnosed in 2008 in the United States, and 3,870 women will die from their cancers.
(Editing by Maggie Fox and Vicki Allen)