Chickens that are vaccinated against bird flu are supposed to be immune to the disease.

But hundreds of chickens at a poultry farm in southern Vietnam have died of avian influenza - even though the farm owner had earlier reported that the birds were vaccinated against the disease, an official said yesterday.

Since late last month, several hundreds of the 3,000 chickens in the flock have died at the farm in Tan Lan commune in Long An province, 50 km west of Ho Chi Minh City.

Last week, they were tested positive for the H5N1 avian-influenza virus, said Mr Dinh Van The, head of the province's Animal Health Department.

The farm owner reported to the department that all birds in the farm had been vaccinated against bird flu, he said.

"We suspect that he was not honest in his report, or that the vaccine used at the farm was of bad quality," he added.

Comment: There is always the possibility that these farmers do not vaccinate their chickens, probably due to the cost and time. But just as likely, they do vaccinate their chickens and this happens, but the media likes to put the "spin" on it using the work "suspect" where they are not saying positively that this is the case, but it locks it in the readers mind that there is a high probability that this is the case when in fact it is an unknown. Don't want it to get out that the vaccines could be ineffective doncha know.

"We are investigating the case."

H5N1 affects mainly poultry and wild birds, but can infect humans who have close contact with sick fowl.

Scientists fear that, if it spreads unchecked, the disease could mutate into a form that could be transmitted between humans, leading to a worldwide epidemic.

Bird flu has killed five people in Vietnam since the beginning of this year.