Live chickens must be banned at markets, academic warns as vaccine loses efficacy

The bird flu vaccine used for local chickens is gradually losing its effectiveness, and total failure is not too far away, a leading microbiologist warned yesterday.

This is happening because the H5 virus, which causes bird flu, is shifting further away from the so-called Fujian strain against which the vaccine was originally effective, the University of Hong Kong's head of microbiology, Yuen Kwok-yung, said.

Professor Yuen, who is part of a team investigating the H5N1 virus found in four wet markets last month, said the city must get rid of all live chickens in markets before the vaccine becomes completely ineffective.

The latest outbreak has already prompted a ban on overnight stocking of live chickens in markets, and the government also wants to buy back all licences from the trade to eliminate live poultry at the sites.

The government has yet to identify the source of the latest outbreak, and it wants to know if the vaccine has become ineffective.

Professor Yuen said existing vaccines have been used in Hong Kong for seven years, but the H5 virus has kept changing. 'It is only a matter of time before it will lose its protection,' he said.

The vaccines protect chickens against the H5 virus by producing antibodies. In 2005, the strength of the antibodies produced by the vaccines in local chickens dropped to only one quarter of the level in 2001, the team has found. Some chickens tested in 2005 had an antibodies level at the 'alarm stage', meaning that the protection was minimal.