Experts are warning of a potentially busy flu season after record numbers were diagnosed with the virus over spring and summer.

A whopping 25,000 Australians have been hit by the illness in the past four months.

Medical authorities are concerned last year’s mild flu season could leave people feeling like they don’t need the immunisation this year.

Griffith University flu expert Professor Paul Van Buynder has told the Herald Sun it is important people aren’t complacent with the shot, because the virus changes each year.

The rise in cases over summer has also prompted debate about whether a second free vaccination should be offered.