A Vietnamese health official says about 600,000 chickens will be vaccinated against a lethal strain of bird flu that has killed more than 40 people across Asia.

The vaccine will be tested on chickens on commercial farms in southern Vietnam. The official says if the inoculations are successful, then birds in other parts of the country will vaccinated.

The vaccine was produced by the French company Merial.

The deadly H5N1 strain of bird flu has killed hundreds of thousands of chickens across Asia since late 2003, as well as 36 people in Vietnam, 12 in Thailand and four in Cambodia.

Many health experts fear the H5N1 strain could mutate into a form that could easily spread between humans, causing a global pandemic that could kill millions.