A new and concerning flu variant, dubbed 'Super-K', has emerged in Australia, causing a spike in flu cases during an unusual time of year. This strain, officially known as the subclade-K variant, has epidemiologists worried about its potential impact on healthcare services.
The timing is everything. While flu seasons typically peak during winter, this variant has shown an unexpected resilience, persisting well into spring and summer.
"The unusual thing here for Australia is the timing," says Patrick Reading, director of the WHO Collaborating Centre for Reference and Research on Influenza. "The symptoms, however, are not so unusual."
Reading explains that the subclade-K variant emerged towards the end of Australia's typical flu season, circulating in September when flu activity is usually low. This led to a prolonged period of elevated influenza cases, extending into the start of summer.
According to the Global Initiative on Sharing All Influenza Data (GISAID), the total lab-confirmed cases of subclade-K in Australia currently stand at 1,083. An Australian Centre for Disease Control (ACDC) report warns that the rapid spread of this variant could put increased pressure on healthcare services over the summer and into the 2026 influenza season.
"Current case numbers for influenza are higher than usual for this time of year compared to previous seasons," an ACDC spokesperson stated.
So far this year, over 4,100 cases of influenza have been confirmed by laboratories, with the actual number of cases likely to be even higher. In comparison, during the first quarter of last year, an average of around 3,300 cases were confirmed weekly.
But what caused this new variant to emerge?
Unraveling the Mystery of Super-K
Adrian Esterman, an epidemiology professor at the University of South Australia, explains that while flu viruses can undergo a large genetic change known as an antigenic shift every few decades, leading to a pandemic, this is not the case with Super-K.
"Super-K is best understood as a drifted version of the familiar H3N2 virus," Esterman said. "It has enough changes to allow it to spread more widely in populations with existing immunity."
The ACDC report suggests that Australian subclade-K viruses may have originated in or been imported from the US, following detections there in June and July last year.
Reading emphasizes that there's no evidence that the variant is more severe than a regular flu, but its ease of transmission is a cause for concern.
"It appears to be slightly less sensitive to antibody or vaccine-mediated protection," he said.
Catherine Bennett, an epidemiology professor at Deakin University, adds that this new subvariant of H3N2 is more immune-evasive due to mutations in the part of the virus that invades our cells, making us more susceptible.
Bennett highlights that while the 2025 flu vaccine included H3N2, it did not cover this specific class. However, the 2026 flu vaccine for the southern hemisphere has already been updated to include this variant and will likely be available around April.
Esterman emphasizes the importance of the flu vaccine, stating that it still significantly reduces the risk of severe disease.
Understanding Australia's Typical Flu Season
"When we get seasonal influenza every year in Australia, it's a combination of three viruses," Reading explained. These include two influenza A viruses (H3N2 and H1N1) and one influenza B virus.
According to the Australian Centre for Disease Control, there were 365,261 reports of the flu in 2024. Cases peaked between May and August and then drastically dropped following winter.
"As we move into spring, flu generally comes down in Australia, and then it's very low during summer," Reading added.
Last year, there were 502,493 reports of influenza, with cases continuing well into the end of the year.
H3N2 subclade-K is estimated to be driving 90% of cases in the United States, according to GISAID.
"What we saw in Australia from September onwards is that the H1N1s and B viruses decreased, but we saw an increase in H3N2 viruses," Reading noted.
Protecting Yourself from the Flu
So, how can you avoid catching the flu?
"People who are unwell should consider testing and should avoid mixing with other people as much as possible," Bennett advised.
She also recommends keeping homes well-ventilated, holding gatherings outdoors if possible, and wearing masks in busy public indoor spaces, especially for those susceptible to more severe respiratory infections.
NSW Health also advises getting the annual flu vaccine and practicing good hand hygiene, including regular handwashing.
With the unusual persistence of the Super-K variant, these precautions are more important than ever.
And here's the part most people miss: while the flu vaccine may not provide complete protection against this variant, it still significantly reduces the risk of severe disease. So, stay informed, stay safe, and don't forget to get your annual flu shot!
