Gwyddoniaeth Ymchwil Tystiolaeth: modelu'r gaeaf 2026 i 2027 - Part 8: UK and international comparison

RSV

During the 2025 to 2026 winter, RSV activity in England started early October 2025 and peaked around mid to late December, which was later than the 2024 to 2025 winter peak in England.

In Wales, a similar pattern was observed with RSV activity starting the week commencing 10 October and peaking early to mid-December 2025.

Sources

• National flu and COVID-19 surveillance report: 2 April 2026 (week 14) - GOV.UK
• Weekly influenza and acute respiratory infection report - Public Health Wales

Flu

During the 2025 to 2026 winter, the influenza-like illness (ILI) GP consultations rate for each UK nation peaked during December before decreasing during January (with a temporary increase in mid-January).

In England, the ILI rate for the 2025 to 2026 winter was similar than that observed in the 2024 to 2025 season up to week 38, and higher than that observed in the 2024/25 season between week 39 and week 51.

In the 2025 to 2026 season, the ILI rates were above the MEM baseline threshold levels for 12 weeks compared with 14 weeks in the 2024 to 2025 season.

In Wales, the GP ILI consultation rate crossed the baseline threshold of 9.6 per 100,000 population in week 46 2025 (week commencing 10 November 2025) and initially peaked in week 50 2025 (week commencing 8 December 2025) at 25.1 per 100,000 followed by a subsequent peak in week 2 2026 (week commencing 5 January 2026) at 26.3 per 100,000.

The GP ILI consultation rate returned below the baseline threshold in week 4 2026 (week commencing 19 January 2026).

The cumulative consultation rate between week 40 and week 14 was:

• 275.5 per 100,000 in 2025 to 2026
• 353.3 per 100,000 in 2024 to 2025
• 182.0 per 100,000 in 2023 to 2024

Northern Ireland had a higher peak ILI GP consultation rate of 57.5 GP consultations per 100,000 than in the winter of 2024 to 2025.

In Scotland the cumulative GP ILI consultation rate for the 2025 to 2026 season (up to week 14) was:

• 282 per 100,000 in 2025 to 2026
• 295 per 100,000 in 2024 to 2025
• 181 per 100,000 in 2023 to 2024

Direct comparisons can not be made between the nations due to the differing methodologies in data collections.

Hospital admissions due to flu reached high levels (according to the MEM thresholds) in England in 2025 to 2026 with a peak of 10.79 weekly admissions per 100,000 (in week 49, 2025).

Scotland and Northern Ireland reached peaks of 19 and 18.1 weekly hospital admissions per 100,000 population respectively in weeks 49 and 49 2025 respectively.

Wales peaked at 190 weekly admissions in week 51 equating to around 5.96 per 100,000 population.

Different data collection methods were used for each nation, so these admission rates are not directly comparable between countries.

The peak hospital admissions in each UK nation is lower than the peak of the winter prior (2024 to 2025), and the peak was earlier in the season.

Flu test positivity peaked at:

• around 21.4% (Respiratory Datamart) for England
• 18.6% for Wales
• 33.4% for Northern Ireland
• 27.5% for Scotland

For all nations the peak positivity rate was lower than for the 2024 to 2025 season but the peak arrived a few weeks earlier than in 2024 to 2025.

Different testing methods were used in each UK nation, so the flu test positivity percentages are not directly comparable between the UK countries.

Sources

• National flu and COVID-19 surveillance report: 30 July 2026 (week 31) - GOV.UK
• Public health data
• Weekly influenza and acute respiratory infection report - Public Health Wales
• Influenza in the UK, annual epidemiological report: winter 2025 to 2026 - GOV.UK

A rapid review of epidemiological data from the southern hemisphere was conducted to help provide additional insight into the upcoming winter season in Wales.

Australia

In Australia, from January to July 2026, there have been 59,779 influenza cases, 74.3% fewer than the 232,805 cases notified over the same period in 2025.

Overall, influenza activity remains lower than at this time in previous years.

Current trends may suggest a return to a more typical pre-pandemic seasonal pattern (for example, 2015 to 2019), characterised by an increase in influenza cases from June and peaking later in winter (around August).

However, it is too early to confirm this.

Throughout 2026, influenza A (unsubtyped) has been the dominant reported influenza subtype across all age groups.

Influenza A(H3N2) notifications have been reported across all age groups, though most notably in children aged 0 to 4 years old.

Influenza B notifications have fluctuated across all age groups during 2026.

However, a small increase has been observed among the 20 to 64 year age group in weeks 27 to 30.

Influenza-like illness notification rates per 1,000 consultations reached their highest level of 2026 at the end of July.

The notification rate remains lower than observed at the same time in 2023 to 2025 and the historical five-year average.

Patients admitted to sentinel hospitals with influenza have mostly been admitted with influenza A (89.4%; 720/805), while 9.4% (76/805) were admitted with influenza B.

In recent severity reporting periods, influenza A(H3N2) admissions have increased, particularly among the 6 month to 4 year and 5 to 16 years age groups.

This is consistent with recent increases in influenza A(H3N2) notifications in the 0 to 4 years age group and rising influenza activity among children reported by community-based surveillance systems in Australia.

COVID-19 has been the leading cause of acute respiratory infection related mortality across the majority of 2020 to 2025; however, between August 2025 and January 2026 the number of deaths in Australia per month involving influenza (both due to and with) were well above usual levels, exceeding COVID-19 deaths.

Since February 2026, deaths in Australia involving COVID-19 have again been higher than those involving influenza.

Source

• Australian Respiratory Surveillance Report – 13 July to 26 July 2026

The WHO currently has 4 Variants under Monitoring (VUMs) as of August 2026.

These variants are:

• BA.3.2
• XFG.1
• PQ.16.1.1
• NB.1.8.1

XFG.1 is currently the variant that is most prevalent globally.

The newest VUM, however, is PQ.16.1.1 which was designated a VUM on 27 July 2026.

WHO state that PQ.16.1.1 is a NB.1.8.1-descendent SARS-CoV-2 lineage, with increasing proportions globally, driven largely by detections in the Western Pacific Region, particularly Singapore.

Considering the available evidence, the additional public health risk posed by PQ.16.1.1 is evaluated as low at the global level.

Its mutation profile may confer additional immune escape, although direct phenotypic evidence is currently limited.

Available surveillance does not indicate increased clinical severity compared with other circulating variants, and existing vaccines are expected to continue providing protection against severe disease.

Sources

• Tracking SARS-CoV-2 variants
• PQ.16.1.1 Initial Risk Evaluation 27 July 2026

Using the international picture to estimate what we may see in Wales, the flu season may see similar figures to 2025 although there could be increased proportion of influenza B and a potential shift in the dominant form of COVID-19.