The 29-year-old woman and 37-year-old man living in areas with reports of unidentified poultry deaths had come down with common flu, said Dr Suphan Srithamma, the ministry's spokesperson.

The woman has already been discharged while the man has succumbed to complications, he said.

As of Friday, 251 people from 42 provinces had been tested for bird flu and none so far had tested positive, he said, adding the lab-test results of 51 patients had yet to come back.

Dr Thawat Suntrajarn, director-general of Disease Control Department, expressed concern about human flu infecting a bird-flu patient, leading to the most feared possibility, in which the two viruses would merge and the highly pathogenic avian flu could then be passed easily from one person to another.

He also reiterated the need for the country to build a plant to produce sufficient amounts of seasonal flu vaccine so that all the high-risk groups of the population could be inoculated, thereby reducing the chances for the human-flu virus to interact with its bird-flu cousin.

Vaccination campaigns have to be carried out yearly since the flu virus is constantly mutating, causing a vaccine to be effective for at most one year, he added.