An experimental vaccine from Merck & Co Inc designed to protect women against a virus that causes cervical cancer has proved effective for up to five years, researchers said on Wednesday.

Women given Gardasil, which Merck is developing with France’s Sanofi-Aventis, experienced no cases of cervical and external genital lesions, the precursors of cancer, scientists told a medical meeting in Paris.

Gardasil is set to compete with GlaxoSmithKline Plc’s rival vaccine Cervarix in what industry analysts expect to be a multibillion-dollar market.

Researchers backed by Glaxo earlier this month reported that women given Cervarix had protection for up to 4-1/2 years.

Both products protect against the human papillomavirus (HPV), a sexually transmitted infection that causes most cases of cervical cancer, the second-most fatal cancer in women.

Gardasil has already been filed for European and U.S. marketing approval, while Glaxo aims to submit Cervarix in the United States before the end of 2006, after filing in Europe last month.

Glaxo estimates the market opportunity for the new vaccines will be 2 billion pounds ($3.57 billion) to 4 billion pounds ($7.14 billion) a year by 2010.