New ‘Super-K’ Influenza Strain Disrupts Seasonal Patterns in Australia
A newly identified influenza strain, dubbed ‘Super-K’ or subclade-K variant, seems to be linked to an unexpected rise in flu cases during spring and summer, according to epidemiologists.
Patrick Reading, director at the WHO Collaborating Centre for Reference and Research on Influenza, noted the peculiar timing for Australia. He told SBS News, “The interesting part is how unusual this is for the season.”
While the symptoms may not be surprising, he pointed out that subclade-K appeared at the tail end of the usual flu season in Australia and New Zealand, peaking around September rather than in the colder winter months. “That led to a spike in flu cases into spring and even early summer,” he added.
Recent data from the Global Initiative on Sharing All Influenza Data (GISAID) indicates that there have been 1,083 confirmed cases of subclade-K in Australia so far this year.
The Australian Centre for Disease Control (ACDC) recently reported that the swift spread of this variant could significantly strain healthcare services throughout summer and into the 2026 flu season. An ACDC spokesperson mentioned that current flu case numbers are surpassing typical counts for this time of the year.
This year, laboratory confirmations have exceeded 4,100 cases, indicating that actual numbers could be even higher. By contrast, around 3,300 cases were documented weekly during the same period last year.
Understanding the Origins of the Subclade-K Variant
Every few decades, flu viruses can experience a major genetic shift, which may lead to pandemics. However, University of South Australia epidemiology professor Adrian Esterman clarified that this isn’t the case with Super-K. Instead, he described it as a variation of the H3N2 virus, possessing enough mutations to spread more effectively within populations that already have some immunity.
The ACDC report suggests that Australian cases of subclade-K may have originated in the U.S., where it was detected in mid-2022. Reading mentioned there’s no evidence indicating that this strain is more severe than typical flu strains; however, it seems to spread easily.
Although the 2025 flu vaccine included H3N2, it does not target this specific subclade.
Bennett emphasized that flu vaccines tend to lose effectiveness over time, so those receiving their shots earlier in the year may not have optimal protection now. On a positive note, she noted that the 2026 vaccine for the southern hemisphere has already been adapted to include this variant and should be available around April.
Esterman reiterated that getting the flu vaccine is still beneficial, significantly lowering the risk of severe illness.
Typical Flu Seasons in Australia
Reading explained that each flu season in Australia generally consists of three virus types: two influenza A viruses, H3N2 and H1N1, along with a B virus. In 2024, the ACDC recorded 365,261 flu cases, predominantly from May to August, followed by a noticeable decline in the summer.
Last year’s flu reports totaled 502,493, with cases extending well into the latter part of the year. GISAID data indicated that approximately 90 percent of U.S. cases are linked to the H3N2 subclade-K variant.
Reading remarked that while H1N1 and B virus cases diminished from September onwards, an increase in H3N2 was observed.
Preventing Influenza Infection
Bennett advised that those feeling unwell should consider testing and try to limit social interactions. “It’s also crucial to maintain well-ventilated spaces, prefer outdoor gatherings when possible, and wear masks in crowded indoor settings, especially if you’re prone to severe respiratory issues,” she stated.
NSW Health also recommends the annual flu vaccine coupled with good hygiene practices, like frequent handwashing.
