Health authorities are issuing urgent guidance as a highly contagious new strain of influenza, dubbed 'Super-K', sweeps through Australia, infecting more than 2,500 people since the start of the new year. Despite its aggressive spread, officials stress that the existing flu vaccine continues to offer strong protection against developing severe illness.
Unseasonal Surge Driven by New Strain
The unseasonably high infection rate for the first week of January is being driven by a mutation of Influenza A (H3N2), known as subclade K or Super-K. This strain was first identified by scientists at Melbourne’s Peter Doherty Institute for Infection and Immunity in September. Genetic mapping suggests Super-K originated in small numbers in the United States in mid-2025 before appearing in Australia in August and taking hold by October.
By mid-November, weekly emergency department presentations for influenza-like illness in New South Wales alone had spiked to over 370. Data from the National Notifiable Disease Surveillance System shows that, in the past seven days, 284 infections occurred in children aged four and younger. More than one-third of Australia's recent cases have been reported in NSW.
Vaccination Rates Plummet Among Vulnerable Groups
Alarmingly, this viral surge coincides with a significant drop in vaccination coverage among those most at risk. The Royal Australian College of GPs reports that in 2025, only 25.7% of children aged six months to five years were vaccinated, the lowest rate since 2021. For those over 65, coverage slipped to 60.5%, a five-year low.
NSW Health Minister Ryan Park cautioned that confirmed case numbers likely represent only a small proportion of the actual population infected, as most people with flu symptoms do not get formally tested. The NSW Respiratory Surveillance Report recorded over 3,000 laboratory-confirmed notifications per week by mid-December, marking a concerning 15% week-on-week increase during a period when flu viruses typically recede.
Vaccine Efficacy and Global Spread
Professor Ian Barr, deputy director of the WHO Collaborating Centre at the Doherty Institute, described Super-K as a "very fit virus" for its persistent spread outside the normal winter season. The strain has now been detected in more than 30 other countries.
The crucial public health message, emphasised since a national alert on 12 December, is that Super-K does not appear to cause more severe disease than previous H3N2 strains; it is simply far more efficient at transmission. Furthermore, research from the European Union indicates the current vaccine's effectiveness against Super-K is "surprisingly better than expected".
The data shows the vaccine was 72.8% effective in preventing hospitalisation in children and 66.3% effective in adults aged 18 to 64. As with most viruses, efficacy was lower in the over-65 group, at 31.7%. Professor Barr affirmed that the current influenza vaccination remains the best available protection against the new strain.
The Australian Centre for Disease Control notes that current case numbers are higher than usual for this time of year. Authorities have warned that the virus's unseasonal persistence could pressure healthcare resources and advise Australians travelling to the northern hemisphere to get a flu vaccine before their journey.
