Influenza cases are rising as Australia moves into spring, following an unusually quiet start to the year. Here’s what is driving the late surge, how this season differs from previous years and what it means for flu vaccination.

The weather is warming up and the hay fever season has begun, but more people are experiencing cases of influenza than expected for spring.

In the two weeks to 6 September, flu cases were up 27 per cent on the previous two weeks. And case numbers are rising.

How is this year’s flu season different?

This year, surveillance systems based in laboratories, data from members of the community, GPs and hospitals all suggest influenza activity has been lower than in previous years for most of the year.

But influenza case numbers have increased since mid-August.

So far, the majority of influenza cases have been due to the H3N2 subtype of influenza A, although some H1N1 and influenza B have also been reported.

The H3N2 subtype has mostly been due to the ‘super K’ strain that was associated with a late surge of cases in 2025. This strain seemed to be more transmissible than usual, although it didn’t cause more severe disease.

There are also some differences in activity in different parts of Australia. New South Wales and Western Australia both had an increase in influenza activity from late June that was not seen in other states and territories.

What is the........

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