China agreed today to share long-sought bird flu virus samples with international health authorities.
It had initially rejected scientists' findings that a new, vaccine-resistant strain was circulating in the country.
The World Health Organization (WHO) said 20 virus samples were being sent to the US Center for Disease Control, a WHO collaborating centre, raising hopes of a better understanding of how the H5N1 bird flu virus is changing.
"We are very encouraged by that. They are viruses from 2004 and 2005, and we will make follow-ups for the 2006 samples," Henk Bekedam, the WHO's China representative, said.
The decision comes after China rejected findings in a paper published last week by Hong Kong and US scientists that said they had detected a new strain of H5N1 in the southern Chinese province of Fujian last year.
The WHO, which says it is still studying the paper, said its understanding had been hampered by China's refusal to share bird flu samples. But China said that when it had co-operated in past, the samples had been misused.
"Four of the five virus samples we provided were used by foreign research institutes in an inappropriate way twice, encroaching upon intellectual property rights of Chinese research institutes," a spokesman said.
Mr Bekedam said the viruses were used in research that did not acknowledge that it was China's Ministry of Agriculture that identified the virus, in breach of scientific protocol.
"That happened twice, and I apologised on behalf of the WHO collaborating centre because that is bad behaviour among scientists," he said.