More than 2,500 Australians have already been infected with a highly transmissible new strain of influenza as the country enters 2026, prompting health authorities to warn that this could become Australia’s worst flu season since national tracking began 35 years ago.
Last year, more than half a million Australians contracted laboratory-confirmed influenza, with 1,508 deaths—a 44% increase on the 2024 mortality rate. Early data from the first week of January suggest the new strain, a mutation of Influenza A (H3N2) known as subclade K and now nicknamed “Super-K,” is spreading rapidly across the country.
First identified in September by researchers at Melbourne’s Peter Doherty Institute for Infection and Immunity, Super-K has also been detected in more than 30 countries. Despite its speed of transmission, experts say there is no evidence that the strain is more severe than previous H3N2 variants. Genetic changes appear to have made it highly efficient at infecting new hosts, rather than increasing the likelihood of serious illness.
Prof Ian Barr, deputy director of the WHO Collaborating Centre for Reference and Research on Influenza, said genetic mapping indicated that Super-K likely originated in the United States in mid-2025 in very small numbers. The strain reached Australia in August, began gaining traction by October, and by mid-November weekly emergency department presentations for influenza-like illness in New South Wales (NSW) had surpassed 370 cases.
NSW alone accounted for more than a third of Australia’s flu cases over the past week. Health Minister Ryan Park cautioned that because most flu cases are never tested, the official figures likely represent only a small fraction of the total number of infections.
Adding to concerns, vaccination rates among the most vulnerable Australians have fallen sharply. In 2025, just 25.7% of children aged six months to five years received the influenza vaccine—the lowest since 2021. Among adults over 65, coverage dropped to 60.5%, a five-year low, according to the Royal Australian College of GPs.
By mid-December, the NSW Respiratory Surveillance Report recorded more than 3,000 laboratory-confirmed cases per week—a 15% week-on-week increase during a month when flu viruses typically decline. “It does seem to be a very fit virus,” Barr said. “Normally we wouldn’t see viruses taking off that late in the season … and we’re still seeing a reasonable number of cases even now in January.”
The Australian Health Protection Committee (AHPC) issued a national alert on 12 December, emphasizing that Super-K is not inherently more severe than previous H3N2 strains, but its unusually high transmissibility could place pressure on hospitals and healthcare resources over the holiday period. The AHPC also recommended that Australians traveling to the northern hemisphere receive an influenza vaccine before departure.
The Australian Centre for Disease Control (ACDC) noted that influenza typically peaks in winter, from June to September. “Current case numbers for influenza are higher than usual for this time of year compared to previous seasons,” a spokesperson said.
Encouragingly, data from the European Union suggest that the current influenza vaccine remains highly effective against Super-K. In children, vaccination was 72.8% effective in preventing hospitalization, and for adults aged 18 to 64, effectiveness was 66.3%. Protection was lower among those over 65, dropping to 31.7%. Despite this, Prof Barr stressed that vaccination continues to offer the best defense against the new strain.
As Australia contends with this early surge, public health authorities are urging Australians—especially the young, elderly, and immunocompromised—to get vaccinated, practice good hygiene, and remain alert for flu symptoms, which can include fever, cough, sore throat, body aches, and fatigue.
With Super-K spreading rapidly and vaccination rates declining, experts warn that 2026 could mark one of the most challenging influenza seasons in decades, underscoring the need for vigilance and community protection.
