GlaxoSmithKline has won US approval to sell a cervical cancer vaccine for girls and young women, while a rival Merck & Co shot was cleared for preventing genital warts in males.

Glaxo said the US Food and Drug Administration cleared the Cervarix vaccine for females ages 10 to 25.

Merck's competing cervical cancer vaccine, Gardasil, debuted on the US market in 2006 and generated some controversy over its cost and potential side effects. On Friday, the FDA approved Gardasil for preventing genital warts in boys and men ages 9 through 26.

Both vaccines fight two strains of the sexually transmitted human papillomavirus (HPV) that cause about 70 per cent of cervical cancers. Gardasil also targets two other HPV strains that cause genital warts. It is unclear how long protection lasts or whether booster shots will be needed.

Some analysts say it will be hard for Glaxo to compete against Merck's three-year head start in the US market. Glaxo's original bid in 2007 stalled when the FDA sought more data.

Cervarix got a boost on Friday by winning the first approval for a cervical cancer vaccine in Japan, the world's second-largest pharmaceutical market after the United States.

Consensus forecasts suggest Cervarix will generate worldwide sales of just over $1 billion in 2013, according to Thomson Pharma, equivalent to about 2 percent of expected Glaxo sales for that year.

Merck's Gardasil had global sales of $1.4 billion in 2008.

The company said Centers for Disease Control and Prevention advisory panel was expected to vote next Wednesday on whether to recommend Gardasil for males.

Both Cervarix and Gardasil fight two HPV strains that cause about 70 per cent of cervical cancers.

In Glaxo's studies, Cervarix was 93 per cent effective in preventing a pre-cancerous condition associated with the two strains. Cervarix also fought some other strains. It was 89 percent effective in preventing precancerous lesions from the third most common HPV type to cause cancer, Glaxo said.

Neither Gardasil nor Cervarix fights all types of HPV.

In the US, cervical cancer is often caught early through Pap smears. Still, about 4,000 US women die each year from the disease. Global deaths from the disease total about 280,000, mostly in developing countries where screening is lacking.

Some critics question if it is worth the cost to vaccinate for cervical cancer when its is largely treatable if caught early. Immunizing boys for genital warts also raised concerns since the warts often clear up without treatment.

Gardasil costs about $360, while Glaxo has not announced a price for Cervarix.

Glaxo said Cervarix should be available in the US later this year. The most common adverse reactions in studies included injection site pain, fatigue and headaches.

FDA advisers in September said Cervarix appeared safe despite miscarriages reported around the time of vaccination and a small number of autoimmune problems such as rheumatoid arthritis and lupus. Panelists urged monitoring after approval to see if there was a link to the vaccine.

Cervarix contains a novel additive designed to boost the immune response. In a Glaxo study, Cervarix produced more antibodies than Gardasil but the researchers did not study if the higher levels provided more protection against cancer.

On Gardasil, the FDA said Merck will run post-approval studies to obtain more information about the safety and effectiveness in men and boys. The FDA has repeatedly said Gardasil remains safe with no unusual complications.

Glaxo shares fell 8 cents to close at $41.20, and Merck shares fell 9 cents to close at $33.21, both on the New York Stock Exchange. – Reuters