Easier Aussie Flu Season May Have Implications for North America

Ran in Medscape, 26 August 2026

By Kevin King, Senior Director, Scientific Affairs, QuidelOrtho

As the 2026 flu season comes to an end in Australia, confirmed cases are down significantly, at approximately 83,000 compared to approximately 500,000 last year, based on data from the National Notifiable Diseases Surveillance System.

The less severe respiratory season could be an early sign of what is in store for the Northern Hemisphere, but a mild start doesn’t always mean a mild finish, according to experts.

The 2025-2026 flu season in Australia and the US was among the most severe in several decades because of the unexpected appearance of the H3N2 variant known as subclade K that was a mismatch for the strains selected for last year’s vaccine.

“The 2025 flu season in Australia was record-breaking, with case counts reaching into the hundreds of thousands,” said Kevin King, PhD, senior director of scientific affairs for QuidelOrtho, a global diagnostics company with products that include influenza testing.

This year’s lower case counts in Australia may be driven in part by the increase in population immunity in the wake of last season, and a better match between the available vaccine and the circulating strains, said King, who works with the surveillance and point-of-care testing data used by hospitals and public health officials to track confirmed influenza cases.

The decline in confirmed influenza cases in Australia this year was not unexpected, King noted. Case counts can shift significantly from one season to the next, and this year’s decline, though notable, is consistent with the typical variability between influenza seasons, he said.

Public health officials and infectious disease experts in the Northern Hemisphere often review Southern Hemisphere flu data as an early indicator of trends for the coming season, said King. “While Australia’s experience can provide valuable information about circulating strains, it does not reliably predict the severity of the US season,” he noted.

“Differences in population immunity, vaccination patterns, healthcare utilization and viral evolution can lead to substantially different outcomes,” he said. However, the Australia case data, in combination with other tools such as wastewater surveillance, can give public health officials additional insight that may help spot a potential outbreak and support a fast and effective response, he said.

To that end, testing remains important each flu season, regardless of mildness or severity, said King. “Accurate diagnostic testing helps patients take the right precautions to protect their communities and receive the treatment they need. Those test results also give health systems and public health officials the data required to manage an effective response,” he said. Overall, traditional seasonality across respiratory illnesses such as respiratory syncytial virus has decreased, as shown in recent studies, which reinforces that need for vigilant testing year-round, rather than focusing only on a defined, respiratory illness season, King said.

More research is needed to determine how best to quickly and accurately detect, manage, and treat the flu to strengthen public health responses, King said. “One promising area of research I’m particularly encouraged by is the use of alternative surveillance approaches, such as monitoring school absenteeism,” he noted. “Researchers at the University of Wisconsin found that symptom-related absenteeism may serve as an early indicator of increased influenza activity in communities, sometimes even before it shows up in clinical testing data,” he said.

“Last year, both Australia and the US experienced a moderately severe influenza epidemic, so I am sure this season has been greeted with some relief down under,” said William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, Nashville, Tennessee.

“A number of factors that likely contributed to last year’s challenging flu season — all of which are not known,” said Schaffner. The subclade K variant was undoubtedly a factor, along with a reduced acceptance of influenza vaccine, he said. “Absent a striking new influenza virus variant, it is likely that the population has substantial immunity, in which case, a current milder season is not surprising,” said Schaffner.

However, “Predicting the severity of flu seasons is a hazardous undertaking,” Schaffner emphasized. “The only thing that is predictable about influenza is that there will be an outbreak every year, causing illness, hospitalizations, and deaths, and much of this is preventable through annual vaccination and prompt treatment,” he said. “While we can hope for a mild flu season, we must prepare for a severe season. Nonetheless, my fingers are crossed, hoping that flu will give us only a glancing blow this winter,” Schaffner added.

Looking ahead, one of the “holy grails” of vaccinology is an influenza vaccine that would protect against many viral strains, provide protection lasting years, and protect against milder and more severe infections, and could be administered without a needle and syringe, said Schaffner. “Many laboratories are working on all of this,” he noted. In the meantime, “clinicians can do more good today if we use our current influenza vaccines more widely,” he said.

King is employed by QuidelOrtho but had no financial conflicts to disclose. Schaffner had no financial conflicts to disclose.