High cost and ethical considerations may impede the introduction of the world's first vaccine to prevent cervical cancer to China, according to Chinese medical experts.

The new vaccine, Gardasil, was developed by Merck & Co Inc in the United States, and won approval from the US Food and Drug Administration on Thursday.

After breast cancer, cervical cancer is the second-biggest killer of women in the world. About 300,000 women die from the cancer worldwide each year. The latest figures released by the World Health Organization (WHO) suggest that nearly 500,000 new cases of cervical cancer are detected annually worldwide.

"The vaccine is a significant advance in the protection of women's health," Acting Food and Drug Administration Commissioner Andrew von Eschenbach said.

Given in three doses over six months, Gardasil targets four types of human papillomavirus (HPV), a common sexually transmitted virus that causes genital warts and most cases of cervical cancer.

Merck said the vaccine would be available within weeks.

China accounts for 20 per cent of cervical cancer victims worldwide, while early detection and treatment has greatly reduced the incidence and deaths in industrialized countries, said Dr Qiao Youlin, who is studying HPV types in collaboration with Merck, WHO's International Agency for Research on Cancer, and the Cleveland Clinic Foundation.

Chinese women don't know much about the cancer. A 2003 survey conducted in the high-incidence area of Xiangyuan County in North China's Shanxi Province found that only 10.3 per cent of the 2,004 surveyed women had heard of a pap smear. Only 4.4 per cent knew that HPV is the primary risk factor in cervical cancer.

As the virus is known to be sexually transmitted, the Gardasil vaccine is to be given to pre-teens before they become sexually active.

"Experts in America and Australia recommend the vaccine be given to boys and girls as young as 9-12 years old while they're still at school," said Dr Elaine Esber, executive director for Merck's Medical Affairs International.

However, some experts are worried the vaccine may trigger an ethical controversy in China.

"Parents might think the practice of vaccinating with Gardasil encourages promiscuity among teenagers," said gynaecologist Liu Zhihua of the Shenzhen Women's and Children's Hospital in South China's Guangdong Province.

Theoretically, Gardasil is effective for women of all ages. "If a woman contracts one of the four types of HPV, the vaccine is still effective against the other three," said Esber. "At this point, however, the vaccine targets 16- to 26-year-old women only. Clinical trials for other age groups between 26-45 are ongoing."

The clinical trials for Gardasil involved 27,000 women and men from 33 countries. China was not included.

The cost of Gardasil will be US$300 to US$500 for a complete series of three shots, estimated Liu, one of many experts who worry the vaccine is out of reach for ordinary people.

Merck submitted its patent application to China's State Food and Drug Administration last February. "We really cannot anticipate when it will be approved for the Chinese market, because each country has its own regulations and procedures," said Jane Lin, medical director for Merck China in Shanghai.

A doctor with the Chinese Academy of Medical Sciences said he did not believe Gardasil will be available in China for at least five years.