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Unintended Consequences

China's plans to vaccinate billions of chickens against avian flu could backfire and end up spreading the disease, poultry and vaccine experts warned last week.

Vaccination teams can easily carry the virus from farm to farm on their shoes, clothes and equipment unless they change or sterilize them each time, the experts said. That could be particularly difficult in a country like China, where the veterinary care system is underfinanced and millions of birds are kept in small flocks by families.

Also, experts said, the task is likely to be overwhelming, because the Chinese eat about 14 billion chickens a year, so mass vaccinations would have to be repeated again and again, while the risk of the disease being reintroduced by migratory birds, in which it is now endemic, would be constant.

Bird vaccination campaigns involve a huge amount of labor because the animals must be injected one by one. China's Agriculture Ministry said last Tuesday that it would inject all of the nation's 5.2 billion chickens, geese and ducks with a vaccine.

Vaccinators were partly to blame for an outbreak of exotic Newcastle disease in California that lasted from 1971 to 1973, Dr. Carol Cardona, a poultry expert at the University of California at Davis, said last week.

In that case, the disease arrived with South American parrots imported for pet stores and spread to commercial poultry farms, but the state tried to vaccinate all "backyard birds," like home-raised poultry.

"It became very clear that the vaccination crews themselves actually spread the virus," Dr. Cardona said. "It's very likely that this may happen in China as well."

For full article, see: DONALD G. McNEIL Jr. "Health Experts Fear Chinese Flu Vaccination Plan Could Backfire." The New York Times, Section 1 (Sun., November 20, 2005): 4.




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