Hong Kong expert warns flu vaccine for chickens losing efficacy

Jul 8, 2008, 4:19 GMT

Hong Kong - A vaccine used to stop outbreaks of the deadly bird flu virus in chickens in Hong Kong for the last seven years is losing its effectiveness, a leading microbiologist warned Tuesday.

Professor Yuen Kwok-yung said the vaccine, which protects chicken from the H5 strain of the virus, is becoming less effective and the city risks further outbreaks because total failure is inevitable.

The head of microbiology at the University of Hong Kong told the South China Morning Post the virus was mutating and shifting away from the Fujian strain of H5N2 that it was developed for.

His warning follows an outbreak of H5N1 virus in four wet markets in Hong Kong in June, the first in years in the former British colony.

Yuen, who is part of a team investigating the outbreak, said the city must get rid of all live chickens in markets before the vaccine becomes completely ineffective.

He said tests showed that in 2005 vaccine was producing only a quarter of the antibodies to protect against the virus compared to the level produced by the same vaccine in 2001.

He said some chickens showed an antibodies level at the 'alarm stage' which meant the protection was minimal.

'It is only a matter of time before it will lose its protection,' said Yuen, who is urging the government to ban all live chicken markets in Hong Kong before the vaccine, developed in the Netherlands, becomes ineffective.

'It takes time for the manufacturers to produce new vaccines,' he said. 'Hong Kong is taking its own risk if it still has live chickens in the markets.'

The government has yet to identify the source of the latest outbreak which resulted in the culling of thousands of chickens and led to tighter restrictions on imports and a ban on overnight stocking of live chickens in markets.

Live chicken sales resumed July 2 after a 21-day ban on import and sales following the outbreak.

Hong Kong was the scene of the first outbreak of bird flu to jump the species barrier in modern times when six people died and 12 others were infected in 1997.

Tough new hygiene and monitoring controls were introduced and Hong Kong has been spared further human infections from the recent bird flu cases across the Asia region.