Pulse ·
Flu came late this spring but it's here now — key facts for September 2026
Influenza activity has risen sharply in Australia after an unusually late season start, with cases up 27% in the two weeks to 6 September 2026. H3N2 is the dominant subtype. The 2026 vaccine reduces the risk of severe influenza hospitalisation by approximately 35%.
Vaccination rates have declined — to 60% in adults aged 65+ (down from 70% in 2022) and just 28% in children aged 2–5. Spring is not too late to vaccinate: anyone without a 2026-formulation flu vaccine should consider getting one now, particularly older adults, pregnant women, young children, and people with chronic medical conditions.
Australia’s 2026 influenza season got a late start. Activity stayed lower than historical norms through the winter months when GPs typically brace for the annual surge, prompting some patients — and perhaps some clinicians — to wonder whether this year’s season might stay mild. It has not.
Cases rose 27% in the two weeks ending 6 September, according to analysis by Monash University infectious disease epidemiologist Allen Cheng, published in The Conversation. H3N2 is the dominant circulating subtype — the same strain family that drove a large outbreak in late 2025. Influenza B and H1N1 are also circulating, but H3N2 accounts for the majority of confirmed cases.
The season is running late. It is not running small. And vaccination rates have dropped in two of the groups that benefit from it most.
What is different about this year
The timing pattern is unusual. In most years, influenza activity in Australia rises through June and peaks in July or August. The 2026 season showed early increases in New South Wales and Western Australia from late June, but the rest of the country remained quiet until mid-August — a full month later than the historical pattern. What that late start has not done is reduce the eventual peak.
The H3N2 variant now dominating is described by researchers tracking influenza genomics as more transmissible than a typical seasonal strain. Severity in hospitalised patients does not appear elevated compared to previous H3N2 seasons, but “more transmissible” in a population where vaccine uptake has declined has predictable consequences for case volumes.
The vaccination numbers tell the clearest part of this story. Uptake in adults aged 65 and over — the group at highest risk of severe disease — has fallen from approximately 70% in 2022 to around 60% in 2026. In children aged 2–5, coverage sits at just 28%. The reasons for declining uptake are not fully understood, but likely reflect a combination of COVID-19-era vaccination fatigue, reduced perceived severity after a series of mild flu seasons, and the practical friction of an annual dose for a disease that, in most adults, resolves without hospital care.
The consequence is a larger pool of susceptible people meeting a more transmissible strain in a season that is still building.
The contested part
The 35% vaccine effectiveness estimate is the figure that will attract the most debate — and the interpretation of it matters.
Thirty-five percent is low by historical standards. Some years, flu vaccine effectiveness against severe hospitalisation runs at 50–60%. A year with a well-matched H3N2 component can do better. This year’s effectiveness is estimated lower, likely because the circulating variant has drifted from the vaccine component selected months earlier when manufacturers committed to the 2026 formulation.
The framing of 35% effectiveness can go two ways. In the frame that says “the vaccine only works a third of the time,” it can feel like inadequate protection and a poor reason to bother. In the frame that says “vaccination reduces your chance of being hospitalised with severe flu by more than a third,” it is a meaningful benefit for every high-risk patient — even if the absolute risk reduction is modest for a healthy 40-year-old.
The honest answer is both framings contain true information and the weight you assign each depends on who the patient is. For a 70-year-old with COPD, 35% effectiveness against hospitalisation is worth pursuing. For a healthy adult with no risk factors who finds the injection inconvenient, the calculus is different — and that is an honest conversation to have.
What is not supported by the evidence is telling patients not to bother. Annual influenza vaccination is an Australian Immunisation Handbook recommendation for everyone aged 6 months and over, with particular urgency for priority groups. Lower-than-usual effectiveness does not become a reason to abandon the advice.
What to do now
Vaccination in September is still worthwhile. The season’s peak is likely weeks away. Anyone who has not had a 2026-formulation influenza vaccine — patients in priority groups in particular — should be encouraged to get one now. Protection develops within two weeks. The Australian Immunisation Handbook remains clear on this.
Priority groups under the National Immunisation Program. Free vaccination is available for people aged 65+, pregnant women, Aboriginal and Torres Strait Islander people aged 6 months and over, children aged 6 months to under 5 years, and people with certain medical conditions including cardiac disease, diabetes, chronic respiratory conditions, and severe obesity. These are the patients who most need an opportunistic conversation if they present before peak season.
Antiviral therapy window. Oseltamivir (Tamiflu) is PBS-listed for adults at increased risk of complications with confirmed or probable influenza. The clinical benefit is greatest when started within 48 hours of symptom onset. Patients in high-risk groups presenting with influenza-like illness should be considered for antivirals early in the consultation, not as an afterthought.
Manage the “it’s just flu” framing. H3N2 has a reputation among patients who lived through 2025 as serious. That perception may now be working in reverse — a late, initially quiet season can reduce the sense of urgency. Patients who recovered easily from last year’s illness may not volunteer that they haven’t been vaccinated this year. An opportunistic question in September consultations takes less than thirty seconds.
Victoria and other southern states are entering the highest-risk period. The window to act — before the autumn consulting room fills up with acute flu presentations — is open now, briefly.
Verdict: yes — flu season has arrived late but with real momentum; an opportunistic vaccination conversation in September general practice consultations is both warranted and timely.
Sources cited
Frequently asked questions
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Is it too late to get the flu vaccine now that flu season has started?
No. Vaccination in September remains worthwhile, particularly if you have not had a 2026-formulation influenza vaccine this year. It takes approximately two weeks to develop meaningful protection after vaccination, but with activity expected to peak in October and November, that window is still open. The Australian Immunisation Handbook recommends annual influenza vaccination for everyone aged 6 months and over, with particular priority for people aged 65+, pregnant women, Aboriginal and Torres Strait Islander people aged 6 months+, people with chronic medical conditions, and children aged 6 months to 5 years. Free vaccination under the National Immunisation Program is available for these priority groups.
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What is H3N2, and is it more severe than other flu strains?
H3N2 is an influenza A subtype that has been associated with more severe seasonal outbreaks than H1N1 or influenza B in some years — particularly in older adults, who tend to have less cross-reactive immunity to newer H3N2 variants. The strain circulating in late 2026 is being tracked as similar to the 'Super K' variant that caused a large surge in late 2025. Researchers have described it as more transmissible than typical strains, though not associated with increased disease severity in hospitalised patients. Vaccine effectiveness against severe hospitalisation is estimated at around 35% for this strain, which is lower than optimal but still clinically significant — particularly for high-risk groups where even a moderate reduction in hospitalisation risk represents meaningful benefit.