It's not ideal to have half of the population unable to use your product, but Merck (NYSE:MRK) is trying to change that for its human papilloma virus (HPV) vaccine, Gardasil.

In addition to causing cervical cancer in women, HPV causes genital warts in both genders, so Merck is trying to get the vaccine approved for use in men and boys in the United States. Based on the results of a clinical trial released today, Merck shouldn't have too hard a time persuading the Food and Drug Administration to expand the label to include this use. The vaccine was 90% effective at reducing the genital lesions compared to placebo.

The company plans to submit the data to the FDA by the end of the year. The move to expand the label couldn't come at a more opportune time -- Gardasil sales have hit a serious roadblock.

 

Q4 2007

Q1 2008

Q2 2008

Q3 2008

Gardasil Sales (in millions)*

$339

$390

$326

$401

Year-Over-Year Increase/(Decrease)

119%

7%

(9%)

(4%)

*As reported by Merck; excludes sales from joint venture with Sanofi-Aventis (NYSE:SNY).

To make matters worse, Gardasil may gain competition in the U.S. from GlaxoSmithKline (NYSE:GSK), which is planning on resubmitting its HPV vaccine, Cervarix, for approval in the first half of next year.

Vaccines have become big business for pharmaceutical companies -- Novartis (NYSE:NVS) and AstraZeneca (NYSE:AZN) saw the writing on the wall and acquired companies to get in on the action. For Merck to get Gardasil back into that high-growth category, it needs to get its label expanded and then be able to persuade older boys and young men that they need the vaccine -- not an easy task with the rising cost of health care.

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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.