Ca Mau, Bac Lieu and Hau Giang are the three provinces where thousands of ducks and chickens have been slaughtered since the latest bird flu outbreaks this year.
Agriculture officials said this week that the risk of recurrence elsewhere was high because of migration of wild birds and poultry smuggling.
The Vietnamese government has ordered animal health authorities and police to tighten control of poultry transport, particularly in the provinces bordering China.
Officials fear that the H5N1 avian flu virus could re-emerge during the lunar new year festival, when poultry consumption rises.
Bird flu has previously killed 42 of the 93 people infected in Vietnam.
The Asian country has the world's second-highest human toll from the disease after Indonesia, where 57 people have died, according to the World Health Organisation (WHO).
The WHO says bird flu has killed 157 people out of 261 infected globally since 2003.