It is not yet proven that Gardasil actually prevents cervical cancer, which can take a decade to develop after HPV infection, because tests of the vaccine before the FDA greenlighted it didn't run long enough to prove that conclusively. "Even though it guards against two HPV strains, the other HPV types need to be taken into account," Smith-McCune says. "It will take a long time before we know the true efficacy of the vaccine."

Even doctors who helped devise the vaccine point out that Pap screening may be more effective in cutting cervical cancer rates. "If we vaccinate every single 12-year-old, it should reduce by half the number of cervical cancers in the next 35 years," says Dr. Diane Harper, director of the Gynecologic Cancer Prevention Research Group at Dartmouth Medical School in Hanover, N.H., and a lead researcher in the development of the HPV vaccine. "With Pap screening, we've reduced it by nearly 75%."

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