Doctors are bracing for a significant outbreak of a deadly flu virus this winter.

Tests on a seriously ill baby admitted to a Sydney hospital this week, have revealed the state's first case of type A virus for this year.

The Type A strain killed thousands of people last winter in the Northern Hemisphere.

World Health Organisation's Influenza Centre deputy director in Melbourne, Allan Hampson, says the virus is reasonably widespread in the population.

He says people aged over 65 or with an underlying heart or lung disease are most at risk.

"The people in the high risk groups, if they haven't been vaccinated yet, then certainly they should be pressing a panic button," he said.

"They should be getting down to their doctors and getting their vaccine because it might be the most important thing they have ever done.

"It can be for those people, a matter of life or death," Mr Hampson said.

http://www.abc.net.au/news/newslink/nat/newsnat-4may2000-96.htm