BEIJING, Aug. 31 (Xinhua) -- China will need up to 400 volunteers for the second trial of a bird flu vaccine, after the first phase of clinical trials showed that it is safe for human use.

The second phase of clinical trials, being considered by the State Food and Drug Administration (SFDA), would test how long the vaccine would protect the human body against the deadly H5N1 virus, said Lin Jiangtao, a leading doctor of the program at the Sino-Japanese Friendship Hospital where the first phase clinical trials took place.

"The second phase will need 300 to 400 volunteers," said Lin, adding that the exact number would be decided by the SFDA.

Results from the first round, which ended in June, showed the 120 people who were vaccinated had no serious adverse reactions.

Lin said some individual cases of mild fever after inoculation were among normal reactions.

The first phase trials indicated a 10-microgram dosage of the vaccine had the best result, stimulating 78.3 percent of protective antibodies, exceeding the European Union standard of 70 percent for a flu vaccine.

The second phase would test similar dosages on volunteers to find out the best procedure to reach the most antibodies, which required a larger pool of volunteers, Lin said.

Prospective volunteers should be aged 18 to 65, but children, people older than 65 or pregnant women will not be accepted.

The vaccine must undergo three phases of clinical trials before being allowed on the market, researchers said.

Sinovac Biotech Limited, which jointly developed the vaccine with the Ministry of Science and Technology and the Center for Disease Control and Prevention, announced earlier this week that it would expand production facilities to produce massive quantities of human bird flu vaccine once the drug passes two more rounds of clinical trials.

Bird flu remains essentially an animal disease, but experts fear that the H5N1 virus could mutate into a form that could pass easily among humans.

The virus has killed 14 people in China since 2003 and 21 Chinese have contracted the virus. Enditem