Not resting on the fact that it had the first approved HPV vaccine, or the free publicity it got for giving it away, Merck (NYSE:MRK) presented data Sunday that its human papillomavirus (HPV) vaccine, Gardasil, is effective in women over the age of the group it was first approved for.

Gardasil is approved in the U.S. for females nine through 26 years of age, but the newest trial results showed that it's effective in protecting women up to the age of 45 against the virus. Merck plans to submit the label-expanding data to the FDA by the end of the year. That would allow it to market it to health practitioners for women up to age 45 toward the end of next year, assuming it gets a standard 10-month review.

The move is clearly a way for Merck to expand the market as competition heats up from GlaxoSmithKline's (NYSE:GSK) Cervarix in Europe, where Gardasil is marketed with Sanofi-Aventis (NYSE:SNY), as well as stateside where Cervarix will likely receive FDA approval early next year.

Merck may have a tough marketing job ahead of it. The big question is whether these women will choose to be vaccinated. The vaccine doesn't cover all the strains of HPV, so women still must have Pap screens regularly. Some may think that because they've lived this long without the vaccine it's unnecessary. I can already imagine the direct-to-consumer advertisements -- mom and daughter going to the doctor together for vaccinations.

The irony of the label expansion is that Merck will be spreading into a market it hopes will shrink. Women need only one series of three shots, and if it's successful at targeting girls and young women, then in 10 to 15 years the number of older women not immunized will be minimal.

Even so, there's no reason to waste the opportunity to vaccinate women now, and Merck seems well on its way.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.