An international panel of experts has rejected the notion that China's vaccination program has caused the bird flu virus to mutate.

The experts from the World Health Organization, the United Nation's Food and Agriculture Organization and the World Organization for Animal Health, were responding to a paper published in the US Proceedings of the National Academy of Sciences. A paper in the Washington, DC-based science journal identified a strain of bird flu virus found in southern China, Malaysia and Laos, calling it a "Fujian-like virus." The paper's authors described it as vaccine resistant.

But the international panel of experts said the "Fujian-like virus" is actually not a new strain and was identified in 2005. The virus mentioned in the report was isolated from poultry samples in 2004, the panel said.

The emergence of mutations in influenza virus is a natural process. There is no scientific evidence backing the theory that H5N1 bird flu virus has evolved as a result of China's vaccination program, said the expert panel, which held discussions from Monday to Friday. David Heymann, interim WHO director, said he appreciated China's cooperative efforts in fighting the disease.