Current Flu in NZ 2025: Season Timing, Strains and Facts

Typical season: May to October (Health NZ) · Peak weekly hospitalisation rate: 16.3 per 100,000 (RNZ) · Flu vaccines received: 1,256,766 people (RNZ) · Community vaccine effectiveness, 2025: 56.8% (95% CI 41.6–68.1%)

Nine data points, one pattern: the season keeps running past its usual window, while vaccination reach stays well below the population it is meant to protect.

What is influenza A?

Influenza A is one of the influenza virus types that cause seasonal flu in humans. WHO’s outbreak notice tied the rise in New Zealand to influenza A(H3N2), and it reported that influenza A was dominant in global activity from October 2025 (WHO (global health agency)).

When New Zealand reporting says “flu” this season, the detail that matters is the subtype, not the general label. The rest of this article follows that thread.

• Influenza A is the type named in the WHO notice behind the 2025 New Zealand rise.
• Seasonal influenza in humans includes several types, so “flu” alone does not identify the virus.

The implication: the strain question is where the answers sit, so the next section starts there rather than with general symptoms.

When is flu season in NZ?

Health NZ’s guidance puts the typical influenza season between May and October, with peak incidence in the winter months (Health NZ (national health authority)). The 2025 season did not stay inside that window.

In the expert reaction published on 26 June 2025, the Science Media Centre (expert commentary) noted that the usual peak had not yet been reached at that point.

• Week ending 22 June 2025: the influenza-positive hospitalisation rate rose to medium activity, per ESR surveillance (Science Media Centre (expert commentary))
• August 2025: subclade K was likely seeded into New Zealand from Australia (arXiv preprint (multi-pathogen NZ study))
• End of August 2025: a late peak in community respiratory illness, particularly on the South Island (PHF Science (national respiratory surveillance))

Activity did not fade on schedule. The arXiv study reports that influenza stayed at unusually high levels into November and December 2025, driven by subclade K (arXiv preprint (multi-pathogen NZ study)).

What sickness is going around right now in 2026?

• Auckland SARI hospitalisations reached “high activity” in the week ending 9 August 2026, higher than any week in 2025 (The Spinoff (NZ online magazine)).
• Hato Hone St John recorded its busiest day on record on 14 August 2026 (The Spinoff (NZ online magazine)).
• Emergency departments saw 15,123 presentations from 10 to 12 August 2026, up from 13,863 the same period the week before (The Spinoff (NZ online magazine)).
• Māori and Pacific peoples were around twice as likely to be hospitalised with influenza in 2025 surveillance (The Spinoff (NZ online magazine)).

Influenza is the virus behind these figures in the reporting reviewed here, and the pressure shows up in emergency departments and ambulance calls, not only in laboratory counts (The Spinoff (NZ online magazine)).

What strain of flu is going around in 2025?

The strain behind the long season has a name. WHO identified influenza A(H3N2) subclade K as the driver of the rise in New Zealand, and reported that subclade K accounted for 89% of Western Pacific sequences in GISAID as of 21 November 2025 (WHO (global health agency)).

The arXiv study describes subclade K as antigenically distinct from earlier H3N2 viruses. That distinctness helps explain why the 2025 season ran long, but it does not show that the strain hit harder (arXiv preprint (multi-pathogen NZ study)).

Why is the new strain of flu so bad?

• Established: subclade K is antigenically distinct and drove the 2025 season, which ran into December (arXiv preprint (multi-pathogen NZ study)).
• Established: subclade K made up 89% of Western Pacific sequences by 21 November 2025 (WHO (global health agency)).
• Not established: the reviewed sources give no severity data for subclade K compared with earlier strains.

The implication: the strain explains the length of the season, not its severity. Readers looking for a severity verdict will find that the evidence stops short of one.

How long does the newest flu last?

None of the reports used for this article gives a duration for the current strain in New Zealand patients. The arXiv modelling covers hospitalisation peaks, not how long individual illnesses last (arXiv preprint (multi-pathogen NZ study)).

Anyone who needs a time frame should check current Health NZ guidance rather than rely on informal estimates.

Is day 3 the worst day of flu?

• None of the reviewed sources tracks flu symptoms day by day.
• No New Zealand duration figure appears in these reports for the 2025 or 2026 strain.
• Any answer about the peak day of illness falls outside what this article can confirm.

The catch: a season can run long at population level while individual illness stays brief, and the reports reviewed here do not separate the two.

What’s worse, influenza A or COVID?

The reports reviewed here do not rank influenza A against COVID-19 for severity. Any ranking that appears without a dated, named source should be treated with caution.

The closest thing to a direct comparison is the 2025 hospitalisation trend, where ESR commentary placed influenza ahead of COVID-19 as the main contributor (Science Media Centre (expert commentary)).

• Confirmed: influenza was the strongest contributor to the rising 2025 hospitalisation trend, per ESR commentary (Science Media Centre (expert commentary)).
• Not established: the relative severity of influenza A and COVID-19 in the 2026 season.
• Not established: which illness is worse for any given age group or vaccination status.

The trade-off: a single severity ranking misses the more useful comparison. The vaccine effectiveness estimates, not a ranking, are what readers can act on this season (Health NZ immunisation handbook (official guidance)).

2025 against 2026

Three reference points, one pattern: both recent seasons ran past the usual window, and the 2022 peak remains the benchmark for hospital rates.

The pattern: the calendar is now a weak forecast, since both recent seasons ran well past the May-to-October window.

Timeline: 2025 to 2026

• Week ending 22 June 2025: ESR surveillance put the influenza-positive hospitalisation rate at medium activity (Science Media Centre (expert commentary))
• August 2025: genomic data suggest subclade K was seeded into New Zealand from Australia (arXiv preprint (multi-pathogen NZ study))
• End of August 2025: a late peak in community respiratory illness, particularly on the South Island (PHF Science (national respiratory surveillance))
• 9 November 2025: WHO reported positivity still high and unusual for the time of year (WHO (global health agency))
• November and December 2025: influenza activity stayed at unusually high levels (arXiv preprint (multi-pathogen NZ study))
• Week ending 9 August 2026: Auckland SARI hospitalisations reached high activity for the first time that year (The Spinoff (NZ online magazine))
• 14 August 2026: Hato Hone St John recorded its busiest day on record (The Spinoff (NZ online magazine))
• Week ending 16 August 2026: Auckland recorded 177 flu hospital admissions, its worst week in a decade (RNZ (public broadcaster))
• Week ending 30 August 2026: the flu hospitalisation rate peaked at 16.3 per 100,000 (RNZ (public broadcaster))
• 6 September 2026: 1,256,766 people had received a flu vaccine (RNZ (public broadcaster))

The implication: the 2025 season ran until December, and the 2026 peak arrived in late August. The calendar gave the wrong answer in both years.

Confirmed facts and open questions

The catch: the open list is longer than the confirmed list. That imbalance reflects the evidence available to this review, not a judgment about the season.

Steps for this season

1. Check the Health NZ flu vaccine data, which is published weekly from 1 April to 30 September 2026 (Health NZ (vaccine programme data)).
2. Plan vaccination from 1 April, the start date Health NZ’s immunisation handbook recommends (Health NZ immunisation handbook (official guidance)).
3. Confirm eligibility for free vaccination if you are 65 or over, pregnant or have certain medical conditions (Science Media Centre (expert commentary)).
4. If you need urgent care, go to an emergency department, which stays open 24 hours, or call 111 (RNZ (public broadcaster)).

The trade-off: waiting for a clearer forecast costs the early-protection window that the 1 April start date is designed to cover.

What officials and experts said

“Influenza looks to be the strongest contributor to the increasing trend in hospitalisations rather than Covid-19.”

Dr Sarah Jefferies, Public Health Physician, ESR, as reported by the Science Media Centre (expert commentary)

“Usually it’s sometime in August or September when we see the peak.”

Allely, emergency doctor, quoted by RNZ (public broadcaster)

The pattern: both voices point to timing, not severity, as the defining story of this season.

What this season leaves open

Related reading: Hand, Foot and Mouth in Adults: Symptoms, Spread and Treatment covers a different infectious illness, for readers looking beyond influenza.

The season no longer follows the calendar most readers expect, and vaccine coverage remained below a quarter of the population by 6 September 2026 (RNZ (public broadcaster)). For people aged 65 and over, pregnant people and those with certain medical conditions, who qualify for free vaccination (Science Media Centre (expert commentary)), the choice is clear: book before the next peak rather than waiting for hospital figures to confirm what the timing already signals.

Related reading: Hand, Foot and Mouth in Adults: Symptoms, Spread and Treatment · North Island New Zealand Thunderstorms: Forecast and Safety

Frequently asked questions