Center for Infectious Disease Research and Policy (CIDRAP) reports that Yuen Kwok-yung (Head of the Microbiology Department, University of Hong Kong), told the South China Morning Post newspaper that the virus is shifting away from the Fujian strain for which it was developed. The comment was reported by Deutsche Presse-Agentur (DPA).

Dr Yuen made it clear to city officials that they must ban all live chickens from markets before the vaccine becomes completely ineffective, according to the DPA report. Tests on birds in 2005 suggested that the vaccine generated only 25% of the antibody response that it did in 2001.

"It takes time for the manufacturers to produce new vaccines. Hong Kong is taking its own risk if it still has live chickens in the market," Dr Yuen said.

In early June, the virus was detected in poultry faeces at several stalls at the market. The reason for the testing has not been explained but since then, poultry cannot be kept overnight at the market and a total ban on live poultry in Hong Kong markets has been proposed.