If 2025 felt like a particularly bad winter for respiratory illness, that's because it was. The data confirms it.
The 2025 record explained
The Australian Centre for Disease Control and the Department of Health published their final season report in early 2026:
- 502,938 lab-confirmed influenza cases notified in 2025 — the highest annual total since influenza became nationally notifiable in 2001
- Approximately 1.5% of the entire Australian population had a notifiable flu infection in 2025 — or 1,525 cases per 100,000 people
- 7,641 hospitalisations for severe acute respiratory infections (SARI), with 3,081 specifically attributed to influenza (the highest of any respiratory pathogen)
- The Royal Australian College of General Practitioners described 2025 as "the worst year on record" for influenza
Subclade K — the variant that extended the season
The 2025 season had an unusual late peak. A new A(H3N2) variant called subclade K emerged mid-season and rapidly displaced the dominant strain. Standard seasonal flu in Australia peaks in July–August and tails off by September. In 2025, subclade K extended significant flu transmission from May right through to November — a six-month season instead of the typical three to four months.
The vaccine produced for the 2025 Southern Hemisphere season was an imperfect match for subclade K. Vaccinated individuals were still protected against severe disease, but transmission was high among unvaccinated and partially-protected populations.
The "tripledemic" effect
2025 wasn't just a flu year. Three respiratory pathogens circulated simultaneously at high levels:
- Influenza A(H3N2) subclade K — driving most adult and elderly hospitalisations
- RSV (respiratory syncytial virus) — driving paediatric admissions, particularly in infants and toddlers
- SARS-CoV-2 (COVID-19) — driving a smaller but consistent stream of hospitalisations across all age groups
The clinical effect of the tripledemic is that any given respiratory presentation in 2025 could have been any of three pathogens, with overlapping symptoms, very different treatment implications, and different infection-control needs. EDs and urgent care clinics dramatically increased point-of-care multiplex respiratory PCR testing through the season.
What 2026 winter might bring
Predictions for the 2026 Southern Hemisphere flu season are necessarily preliminary, but three factors are being watched:
- Subclade K immunity carryover. A meaningful portion of the 2025-infected population now has some immunity to subclade K. If the variant persists into 2026 without further drift, total cases should be lower.
- 2026 vaccine match. The Southern Hemisphere influenza vaccine formulation for 2026 includes updated H3N2 strains designed to better cover subclade K and its descendants. Match quality won't be confirmed until mid-2026 data comes in.
- Northern Hemisphere signals. A early-2026 decrease in influenza activity continued into January, but a separate Welsh modelling study suggests acute respiratory illness hospital admissions will remain elevated through 2025–26. Australia typically follows Northern Hemisphere patterns with a six-month lag.
Vaccination — the 2026 trio
The 2026 winter vaccination programme in Australia includes three respiratory vaccines for many adults:
- Seasonal influenza vaccine — free for at-risk groups under the National Immunisation Program; available to anyone via private purchase
- COVID-19 boosters — recommended for over-65s and immunocompromised, available for others
- RSV vaccines — newly funded in 2025 for over-75s and pregnant women (RSV vaccine in pregnancy protects newborns)
You can have all three on the same visit if eligible. Co-administration is well-tolerated.
When respiratory illness needs immediate care
Most flu, RSV and COVID infections are managed at home with rest, fluids and paracetamol. The clinical features that warrant same-night assessment are:
- Breathing fast, laboured, or with effort (any age)
- Any baby under 3 months with a fever of 38°C or more
- Drowsiness, floppiness, or refusing to drink in a child
- Chest pain or pressure
- Confusion (particularly in older adults)
- Severe dehydration (no urine output for 8 hours)
What this means for our clinic in 2026
We are expecting a busy winter regardless of whether 2026 matches the 2025 record. The structural reality is that respiratory illness peaks across May–September in Australia, public ED capacity is stretched at the best of times, and Cat 4/5 winter presentations (mild asthma exacerbations, otitis media in kids, scripts and dressings while unwell) are exactly our scope. Phone us first — phone triage is free and we can usually tell you in five minutes whether we're the right place for what you've got.