Trials of the vaccine were launched last December and some 120 Chinese volunteers have since received shots of the experimental immunization against the deadly virus, the Xinhua news agency said Monday.

The participants, previously reported to be healthy people aged between 18 and 60 from Beijing, have shown "no serious adverse reactions," researchers were cited by Xinhua as saying.

Results showed that the vaccine successfully stimulated the production of antibodies in the participants to fight the virus, Xinhua cited the vaccine manufacturer, Beijing-based pharmaceutical firm Sinovac Biotech Co., as saying.

The company jointly developed the inoculation with China's Ministry of Science and Technology and China's Center for Disease Control and Prevention.

Sinovac said the 10 microgram dosage of the vaccine proved most effective, stimulating 78.3 percent protective antibodies, exceeding the European Union standard of 70 percent for a flu vaccine, according to Xinhua.

Another phase of clinical trials will need to be conducted before the vaccine can be approved. It was expected to take at least a year before the vaccine finishes its two-phase clinical trials.

If approved, it will first be used on high-risk groups such as veterinary and laboratory workers and poultry farmers in afflicted regions, a company official had said.

It would also be cheaper than normal flu jabs.

Various companies around the world are trying to develop a vaccine against the virus, but the
World Health Organization's top official in China has said vaccines might be useless in the event of a bird flu pandemic as the virus would have mutated.

It was difficult to predict how the virus would mutate and it could take months before a new vaccine was then produced, the official has said.

The H5N1 virus circulates among wild birds and poultry and can be passed to humans, normally those who come into contact with such animals. The disease has killed about 140 people, mostly in Asia, since 2003.

Twenty-one people in China have contracted bird flu, and 14 of them died, with the most recent fatality occurring in July, according to official figures.

Source: AFP