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China H5N1 outbreak puts vaccines under spotlight

Written by: Staff

HONG KONG, Mar 17: The discovery in southern China of healthy-looking chickens that are infected with the deadly H5N1 bird flu virus has raised fears among experts that vaccines used in the country are substandard.

Bad vaccines for poultry can ''mask'' diseases. The vaccines protect birds, which often don't show symptoms, but do not guard against infection and the birds can shed the virus in their faeces.

The virus then spreads to more birds, mutates and can even jump species barriers, for example, into humans.

In a 2004-2005 survey, researchers found seemingly healthy but H5N1-infected chickens in poultry markets in south China, including Guangdong, just north of Hong Kong.

The development is unsettling. Chickens usually die within 24 hours of being infected with H5N1, but without signs of disease, the virus is harder to detect, control and also much easier to pass on to unsuspecting humans.

The risk of such asymtomatic poultry came to the fore earlier this month when a man died in Guangdong after visiting several live poultry markets and officials later said he probably caught the disease from live but H5N1-infected birds.

Experts are now asking hard questions about the quality of China-made vaccines.

''With this finding of asymptomatic birds, we have to ask if this is because of the vaccines they use, a mutation of the virus? The issue of vaccines has to take top priority,'' said Hong Kong infectious disease expert Lo Wing-lok.

The World Health Organisation, which backed China's plan to vaccinate billions of poultry last year, is also concerned.

Julie Hall, in charge of the WHO's outbreak response in China, said recently that studies were needed into see if China's vaccination programme might be ''masking'' the virus, which has killed about 100 people in Asia and the Middle East since 2003.

China's Harbin Veterinary Research Institute, which is linked to the Ministry of Agriculture, makes flu vaccines for poultry. The ministry approves these vaccines and controls their sale and distribution.

''Because information is not abundantly available, there is speculation the vaccines may not be as effective. It is up to the Chinese authorities to be more transparent,'' Lo said. China's Ministry of Agriculture (MOA) has declined comment.


An expert familiar with the situation said: ''MOA is the only place allowed to develop, manufacture and distribute vaccines.'' ''It is not the best vaccine. It can save the bird's life but it can't stop the virus from replicating. The bird looks good, but it has the virus. If you bring it into an unvaccinated area, other birds die and people (who contract the virus) die,'' the expert said.

''Places like Vietnam and Thailand are importing these Chinese vaccines. So what is happening in China (asymptomatic poultry) can happen in these places soon,'' said the expert.

But Vietnam, which has had no new bird flu outbreaks in poultry or humans since November, is not overly worried. It says the China-made vaccines must pass quality-control tests.

''We have been using Chinese vaccines nationwide and there has been no problem regarding quality,'' said Hoang Van Nam, deputy director of the Agriculture Ministry's animal health department.

''We have just completed tests of 20,000 poultry nationwide and found no trace of bird flu,'' Nam said. Neither has the department found any asymptomatic chickens.

Although Thailand bans H5N1 vaccination in chickens, there have been reports of police seizing vaccines being smuggled along the Mekong river from China. But nobody knows if they have been smuggled in successfully and used.


Although China has been vaccinating its farmed poultry in the past few years, that has not stopped the virus from proliferating and mutating. After scientists first isolated H5N1 in a goose in Guangdong in 1996, the virus has continued brewing and there are now five dominant subtypes in southern China.

In the past year, H5N1 has spread across 14 Chinese provinces and regions, and penetrated parts of the Middle East, Europe and Africa after infecting many parts of Asia since late 2003.

Although migratory birds probably carried the virus from China's Qinghai Lake to Africa and Europe, microbiologist Guan Yi from the University of Hong Kong believes that the spread of the virus in southern China is due largely to domestic poultry.

''The virus outbreak in south China is not caused by migratory birds, but domestic ducks and geese and maybe chickens,'' he said.

Guan, whose laboratory has genetically sequenced strains of the virus found in many parts of the world, believes live poultry exports from southern China probably introduced the virus into Vietnam, Thailand, Malaysia and Indonesia.


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