Doctors issued the warning after 2025's record season, during which more than half a million Australians were infected and 1738 killed, outstripping COVID-19 deaths for the first time since the pandemic.
Almost 29,000 Australians have already contracted flu in 2026, barely half the number of those diagnosed by this point in 2025.
But that was a poor indicator of the flu season's outlook, hospital operator Mater's infectious disease director Professor Paul Griffin said.
"Drawing comparisons ... could lull us into a false sense of security," he told AAP.
"I don't think we've seen anything that should make us think we're in a better position than last year."
January 2026 was almost three times deadlier for flu sufferers than the first month of 2025, with 101 people succumbing to the disease during an unusual persistence through summer, according to the Australian Bureau of Statistics.
A new strain nicknamed "Super-K" has also alarmed scientists by appearing earlier, spreading faster, and appearing more resistant to human immunity and vaccines, an Australian Centre for Disease Control spokesperson said.
"It's a type of flu that's changed quite significantly," Prof Griffin said.
"When that change is more significant, protection from past infection and vaccination doesn't quite work as well."
Vaccination rates are among the best predictors of how bad a season will be, Royal Australian College of General Practitioners' Victoria state chair Dr Anita Munoz said.
By September 2025, the number of children younger than five - a vulnerable group - who had received the flu vaccine had plummeted more than 40 per cent from 2020, according to the National Centre for Immunisation Research and Surveillance.
Less than one-third of all Australians received the flu jab in 2025.
Dr Munoz said "vaccination fatigue" and complacency had cooled Australians' attitudes to immunisation post-COVID.
"People are still genuinely disgruntled by their experiences in the pandemic," she said.
Flu cases nosedived in 2020 and 2021 as a side effect of COVID-19 restrictions, but have had four record-breaking years since normal life resumed.
It's hoped a new nasal spray vaccine will help bring youngsters afraid of needles back into clinics.
Kids up to 11 years old in varying age ranges can access the jab-free vaccine at no cost in NSW, Queensland, Western Australia and South Australia.
Others younger than 18 will have to cough up about $50 to $70, but doctors want expanded access.
"It's unacceptable that your access to vaccines can be determined by the state in which you live or the postcode in which you live," Dr Munoz said.
Meanwhile, traditional injections remain free nationwide for children younger than five, adults older than 65, pregnant women, Indigenous people and those with serious health conditions.
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