More than 2,500 Australians have contracted a highly transmissible new strain of influenza, known as Super-K, in the first week of January, raising fears of the country's worst flu season since records began 35 years ago. The strain, a mutation of Influenza A H3N2 called subclade K, was first identified in September by scientists at Melbourne's Peter Doherty Institute for Infection and Immunity.
Health authorities have stressed that Super-K does not appear to cause more severe illness than previous strains, but its genetic changes allow it to spread rapidly. Vaccines remain effective against severe disease, though vaccination rates have plummeted among vulnerable groups. In 2025, only 25.7% of children aged six months to five years were vaccinated, the lowest since 2021, and rates for those over 65 fell to 60.5%, a five-year low.
Data from the National Notifiable Disease Surveillance System shows 284 infections in children aged four and younger in the past week. New South Wales has reported over a third of Australia's cases, with weekly emergency department presentations for flu-like illness spiking to over 370 in mid-November. The state health minister, Ryan Park, noted that many cases go untested, so the true number may be higher.
Prof Ian Barr, deputy director of the WHO Collaborating Centre for Reference and Research on Influenza, said genetic mapping suggests Super-K originated in the US in mid-2025 and began appearing in Australia in August. By December, NSW recorded over 3,000 lab-confirmed notifications a week, a 15% week-on-week increase during a month when flu typically declines.
The Australian Centre for Disease Control said current case numbers are higher than usual for this time of year. The Australian Health Protection Committee warned on 12 December that the strain's persistence could pressure healthcare resources over the holiday period. Travellers to the northern hemisphere are advised to get vaccinated.
Research from the EU shows the current flu vaccine is 72.8% effective in preventing hospitalisation for children with Super-K, 66.3% for adults aged 18–64, and 31.7% for those over 65. Prof Barr said the vaccine remains the best protection available.
