"If the vaccination delays to beyond November 15, it will be very dangerous because the winter is the season of flu," the paper quoted Agriculture Minister Cao Duc Phat as saying.

Vietnam requires farmers to keep vaccinated birds for 28 days before putting them on sale to make sure the injected birds are healthy.

Bird flu has killed 43 people in Vietnam, with 22 of the victims dying since the H5N1 virus, which first swept through much of Asia in late 2003, returned in December 2004.

It has also killed 12 people in Thailand, four in Cambodia, three in Indonesia and spread to Kazakhstan and parts of Russia where health workers found mass bird deaths in what could become the first case of the deadly virus spreading to Europe.

There have been no reports of human infection in Russia.

Vietnam has been vaccinating poultry against bird flu since July 31 in one province in the southern Mekong Delta and another in the north.

The Agriculture Ministry said poultry in the remaining 11 Mekong Delta provinces and birds in Ho Chi Minh City would be vaccinated from September.

State media said 100 million batches of poultry vaccine were being imported from China and the Netherlands to ensure all birds in the regions with high risk of infection, such as the Mekong Delta, would be injected.

Vietnam now has around 210 million poultry.

Health experts said the virus is now endemic in parts of Asia, including Vietnam and Thailand, despite the deaths or slaughter of tens of millions of domestic fowl.