May 9, 2007 -- The Gardasilvaccine is extremely effective in protecting women against precancerous lesions caused by the human papillomavirus types (HPVs) that cause 70% of cervical cancers and most cases of genital warts.
That's the good news from two huge, international clinical trials. The not-so-good news: Among sexually experienced 15- to 26-year-old women -- some of whom already have HPV infection -- the vaccine is far less effective in protecting against dangerous cervical lesions.
The FUTURE 1 trial enrolled nearly 5,500 women aged 16 to 24. The FUTURE II trial enrolled more than 12,000 women aged 15 to 26. Three-year results from both trials appear in the May 10 issue of The New England Journal of Medicine.
Gardasil protects against HPV that is spread mainly during sex. Women often get HPV infections soon after beginning sexual activity, although most HPV infections will not develop into cancer. So the best time to get the vaccine is in the pre-teen years, before age 13.
Or even sooner: The FDA has approved Gardasil for 9- to 26-year-olds, and the CDC has added it to the childhood vaccination schedule. Several states are debating making HPV vaccination mandatory for public school attendance, although all of these measures allow parents to opt out.
In the current studies, the vaccine looked very safe -- and very effective, says FUTURE II investigator Kevin Ault, MD, associate professor of gynecology and obstetrics at Atlanta's Emory University.
"The vaccine's efficacy is the biggest news," Ault tells WebMD. "In FUTURE I, it was 100% effective in preventing precancerous lesions and genital warts, and in FUTURE II it was 98% effective in protecting against high-grade, precancerous cervical lesions."
Ault's numbers reflect the vaccine's effectiveness against the four HPV strains included in the vaccine -- including cervical-cancer-causing HPV-16 and HPV-18.
But these are only two of the 15 HPV strains known to cause cervical cancer. An editorial accompanying the studies notes that overall, the vaccine was no more than 20% effective in protecting women against high-grade precancerous lesions.
"This gives us a glimpse of what to expect from vaccinating a generation of 15- to 26-year-olds regardless of their sexual exposure," the editorial's co-author, Karen Smith-McCune, MD, tells WebMD. "In that general population, looking at all women who got the vaccine with all types of HPV exposure, efficacy in reducing precancer was modest -- 17% fewer cases of precancer in vaccinated women vs. the placebo group. And if you look at the most significant precancer, grade 3, there is no significant reduction among vaccinated women."