The first vaccine to prevent cervical cancer won U.S. approval on Thursday when health officials cleared a Merck & Co. Inc. shot to block a sexually transmitted infection that causes the deadly disease.

Public health experts called the Gardasil vaccine a major advance against a disease that kills about 300,000 women worldwide annually. Industry analysts said the product also should help revive the fortunes of struggling Merck with annual sales that could top $2 billion.

The vaccine blocks infection with certain types of the human papillomavirus (HPV), which causes genital warts and most cervical cancer.

This vaccine is a significant advance in the protection of women's health in that it strikes at the infections that are the root cause of many cervical cancers, acting Food and Drug Administration Commissioner Andrew von Eschenbach said.

Given in three doses over six months, Gardasil targets four HPV types believed to cause more than 70 percent of cervical cancer cases and 90 percent of genital warts. The vaccine was approved for use in girls and women ages 9 to 26, Merck said.

The catalog price for Gardasil will be $120 per dose, the company said.

The approval puts Merck ahead of GlaxoSmithKline Plc, which is developing its own HPV vaccine called Cervarix and plans to apply for U.S. clearance this year.

Most cervical cancer deaths occur in developing countries. In the United States, widespread screening catches the disease early when it is treatable, but about 4,000 women die from it each year.

Merck is counting on Gardasil to help revive earnings growth in the face of more than 11,500 lawsuits over its recall of arthritis drug Vioxx.

Jason Fox, an analyst with H&R Block Financial Advisors, said Merck still faces several challenges, such as expected generic competition later this month to its blockbuster cholesterol treatment Zocor, but Gardasil's approval lends stability to the company's situation.

Our bigger picture view of Merck is they really need Gardasil, Fox said. This is their biggest pipeline opportunity in the next year.

Shares of Whitehouse Station, New Jersey-based Merck gained about 5 cents to $34 in afternoon trading on the New York Stock Exchange.

(Additional reporting by Lewis Krauskopf in New York)