The H5N1 bird flu virus that killed hundreds of unvaccinated and vaccinated birds in a Yuen Long farm in just a few hours was the Fujian strain, a further indication that the virus is local. Undersecretary for Food and Health Gabriel Leung confirmed yesterday the finding of the Fujian strain - or clade 2.3.4 in World Health Organisation parlance - which first emerged in Fujian and has been the dominant type of H5N1 bird flu found in Hong Kong since 2002. In the latest outbreak discovered on December 8, the flu killed 285 chickens, while about 68,000 chickens and 26,000 eggs were destroyed. A second uninfected farm within a 3km radius was also quarantined. Trade in fresh chicken has been banned for 21 days. 'We haven't seen a significant change in the genetic sequencing [of the strain],' Professor Leung told a special meeting of the Legislative Council panel on food safety and environmental health. 'Of course, it can spread disease, but that is not a significant change in the strain. But we will have to look at more details of the report,' He said that a more detailed study would delve into the strain's 'antigenecity'. An antigenic shift could signal a possible drift towards more efficient transmission among humans. A vaccine study group is also investigating if the H5N2 vaccine used for five years was failing, he said. Professor Leung also rejected as 'ridiculous' comments in the farming community that the outbreak had been 'deliberately' set off by the government. According to a report submitted to the World Organisation for Animal Health (OIE) by the Agriculture, Fisheries and Conservation Department on December 12, the farm had 67,968 chickens and 25,680 fertilised eggs, and with the discovery all were culled in a two-day operation on December 9 and 10. At the panel meeting yesterday, Thomas Sit Hon-chung, the department's assistant director, did not refer to the OIE report, but said smuggled eggs could not have been the source of the outbreak. Professor Leung also rejected suggestions that chicken farms should no longer use unvaccinated birds as sentinel similar to the practice on the mainland, which has seen more outbreaks of bird flu and human infections than Hong Kong since 2003. He said the sentinel birds acted as early signals for bird flu infections. This week, the mainland announced it had killed 377,000 chickens after an outbreak of bird flu was discovered in two areas of Jiangsu province . He also said that although the ban on fresh chicken trade would end on December 30, the authorities would assess the situation in Hong Kong, the mainland and the region before resuming the trade. The government will also consider whether overnight stocking of live chickens at the Cheung Sha Wan wholesale market should be banned, too.