A Chinese company that is developing a H5N1 bird flu vaccine for humans plans to kick off a second clinical trial before the end of the year and will have its production capacity expanded ten-fold by mid-2007.

"The second clinical trial should be over by July or August next year, just before the flu season begins," Yin Weidong, managing director of state-backed Beijing Sinovac Biotech Co., told Reuters in an interview on Thursday.

He tried to ease concerns over using a strain of the virus found in Vietnam in the vaccine, saying it would offer some protection against other H5N1 strains.

The company needs to obtain the approval of the State Food and Drug Administration (SFDA) for the second trial and will file its application with the agency within the next two weeks.

"The government values this project very highly and it will get going faster," Yin said. He added that the World Health Organisation had provided advice in the first clinical trial and would probably do so again in the second trial.

Sinovac ran its first clinical trial involving 120 volunteers in Beijing this year.

It published its findings in The Lancet medical journal in September, saying the experimental vaccine was effective and well tolerated at low doses.

It used whole-virus vaccine in 1.25, 2.5, 5 and 10 microgram amounts, but the 10 microgram dose was found to be most effective in producing an immune response.

The volunteers, aged between 18 and 60, did not suffer serious side effects, but some experienced pain, swelling and fever.

The second trial will have a wider age limit, taking in people below 18 and over 60, but Yin said the drug administration would make the final decision.

Apart from Beijing, Sinovac will look for volunteers in two other cities, most likely in southern China. There will be two dosages: 5 and 10 micrograms.

By mid-2007, Sinovac will have expanded its production capacity to 20 million doses from a current 2 million, but when the vaccine goes into production will hinge on how soon it secures orders.

Sinovac and several companies around the world are in a race to develop a vaccine to combat what experts fear would be a flu pandemic triggered by the H5N1 bird flu virus, which has killed 148 people since late 2003.

Although it remains a disease among birds, scientists say it could wreak havoc and kill millions if it mutates and learns to transmit efficiently among humans.

Some experts, however, question the rationale behind designing these "pre-pandemic vaccines" based on a H5N1 strain found in Vietnam in recent years, saying they might not protect against other H5N1 strains and the eventual pandemic strain.

At least two other H5N1 strains have become geographically more widespread; with one spreading across not only Asia, but parts of Europe, Africa and the Middle East.

But Yin said there should be some amount of cross protection.

"Even though the virus is changing, it is still H5N1. We are facing one enemy," he said.