GlaxoSmithKline has unveiled plans for a head-to-head study of cervical cancer vaccines that will pit its candidate Cervarix directly against Merck's rival offering Gardasil.

The independent, random study will be conducted in the US among 1,042 women between the ages of 18 and 45. The results are expected 12 months after enrollment for the study is completed.

"Nobody has done this before so this is quite a bold step," said Peter Cartwright, pharmaceuticals analyst at Evolution Securities in London. "Clearly GSK is confident that their data will be better."

After breast cancer, cervical cancer is the second most frequently occurring form of cancer in women between 20 and 39. In 2006, nearly 10,000 women were diagnosed with the disease.

GSK plans to seek regulatory approval for Cervarix from America's Food and Drug Administration by April.

"Vaccination to prevent cervical cancer may be the most significant healthcare breakthrough for women in our lifetime," Mark Blatter, medical director of primary physicians research in Pittsburgh, said.

Dr Blatter added: "This unprecedented trial, which will enrol more than 1,000 women, will provide the first scientific evidence to demonstrate how the two vaccines differ with respect to inducing strong and sustained immune responses in women who may be appropriate for vaccination."

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