H5N1 virus

Flu cases prompt new look at vaccine

PUBLISHED : Thursday, 22 December, 2011, 12:00am
UPDATED : Wednesday, 06 May, 2015, 4:32pm


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The efficacy of avian flu vaccines has come under question amid fears of the return of an avian flu outbreak in Hong Kong.

Following the identification of the virus in a dead bird found in the Cheung Sha Wan Temporary Wholesale Poultry Market, scientists at the University of Hong Kong are analysing DNA samples from the dead chicken and live birds to determine if there are any major mutations in the virus that would undermine the effectiveness of vaccines. Results are expected within a few days.

By late last night, 19,451 birds at the market, including 15,569 chickens, had been culled after one chicken found dead at the market tested positive for the deadly H5N1 bird flu. The suspension of live chicken supplies for 21 days until January 12 increased the demand for chilled birds by families preparing for the winter solstice festival tonight.

The World Health Organisation yesterday also confirmed it had been informed by the Hong Kong government about the discovery of at least one infected chicken.

'The culling was decided by the Hong Kong authorities,' said Timothy O'Leary, spokesman for the WHO's western Pacific office. 'Culling is a recommended way to reduce the risk to humans and to prevent further spread of the virus among chickens.' University of Hong Kong chair professor of microbiology, Dr Yuen Kwok-yung, said the team had been aware of changes in the virus two years ago and there had been discussions on whether Hong Kong would need a new vaccine.

'However, making a new vaccine is very costly,' Yuen said. 'We have to monitor the situation to determine if it is justified to make changes.'

His colleague, Dr Leo Poon Lit-man, an assistant professor of the university's school of public health, said he believed the current vaccine was still effective, though assessing its strength would require more analysis. He said it would take years to develop a new vaccine.

'There are possibilities that the vaccine remains effective, but wrong dosage or misuse of the vaccines has undermined its efficacy,' said Poon, who specialises in influenza biology, emerging animal viruses and vaccinology. 'So, we should be patient and wait for the test results before deciding the next step.'

Meanwhile, Secretary for Food and Health Dr York Chow Yat-ngok said the government had been using a vaccine from the Netherlands for the H5N2 strain of bird flu, along with a vaccine from Harbin . But he said it was time to review whether the two vaccines remained effective. He said the dead chicken that tested positive for avian flu was sick before it arrived in the market. But it was unknown whether it was from the mainland or one of 30 local farms.

'We are now studying whether more measures will be needed to help track down the source, such as requesting all farms to attach a label to each chicken on its feet,' he said.

The government had visited all 30 chicken farms across the city and so far, there were no reports of suspected outbreaks of avian flu.