路透社：Trial of H5N1 vaccine effective in low doses

LONDON (Reuters) - Low doses of an experimental Chinese vaccine against the H5N1 bird flu virus produce an immune response in healthy people, according to early trial results reported on Thursday.

The vaccine made by Beijing-based Sinovac Biotech Co. Ltd contains a modified version of the whole virus plus an adjuvant, or additive, to increase effectiveness.

Results of the trial published online by The Lancet medical journal show it was effective and well tolerated at low doses. Dosage is important because if a small amount of vaccine is effective it will allow more people to be vaccinated.

"During a pandemic, the demand for influenza vaccines will far outstrip the manufacturing capacity of such vaccines, a situation that has led to WHO (the World Health Organization) encouraging investigation into dose-sparing strategies, including the use of adjuvants and whole virion vaccine," said Weidong Yin, one of the authors of the study.

"Our trial suggests that an H5N1 vaccine manufactured and formulated with both of these approaches is well tolerated and immunogenic," he added.

Several companies around the globe are developing and testing vaccines against pandemic influenza. Scientists fear the H5N1 bird flu virus could mutate into a pandemic strain capable of killing many millions of people.

The Sinovac Biotech vaccine was developed by the Chinese Centers for Disease Control and Prevention and supported by China's Ministry of Science and Technology.

Researchers gave 120 volunteers aged between 18-60 years old two doses of a placebo or the whole-virus vaccine in 1.25, 2.5, 5 or 10 microgram amounts plus the adjuvant aluminum hydroxide.

All the vaccine doses produced an immune response after 56 days but the 10 microgram dose was the most effective.

The researchers said the volunteers did not suffer any serious side effects but some experienced pain, swelling and fever.

In a commentary on the findings Ian Stephenson, of the infectious diseases unit at the Leicester Royal Infirmary in England, said vaccination will be a vital element in dealing with a pandemic influenza virus.

"These findings identify a potential dose-sparing approach that could be crucial for a global supply of pandemic vaccine," he added.

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