Gwyddoniaeth Ymchwil Tystiolaeth: modelu'r gaeaf 2025 i 2026 - Part 1: summary

Winter respiratory viruses consistently increase pressure on NHS Wales, though their impact varies each year. Uncertainty remains due to factors such as concurrent viral peaks and the effectiveness of seasonal vaccines.

This paper presents modelled scenarios based on historical data to support winter 2025 to 2026 planning for NHS Wales. It estimates potential pressures on hospitals (in terms of admissions and bed occupancy) from seasonal respiratory viruses, with a focus on influenza, RSV, and COVID-19. Whilst COVID-19 is not strictly a winter virus, overlapping peaks with flu and RSV could compound demand on healthcare services.

The paper also examines wider impacts of winter pressures across NHS Wales beyond hospital admissions, including emergency department attendances, and primary care activity due to respiratory illnesses. It highlights trends in GP consultation rates for acute respiratory infections and provides estimates of vaccine uptake for flu, RSV, and COVID-19 among eligible groups.

As with all modelling, the scenarios in this paper are not a prediction of what will happen but estimates of what could happen. We could also see similar peaks occurring at a different time in the season. The modelling uses past data to estimate future projections. Any changes to the NHS system, particularly in the past 12 months, may not have been taken into account in the modelling.

An expected increase in health care demand over the winter period may lead to a number of risks. The five harms framework, can be used to assess where risks could arise from, outlined in Table A1 (Appendix). The five harms framework was originally developed to assess the potential impact of the COVID-19 pandemic and can be explored further in the Technical Advisory Group paper - Five harms arising from COVID-19: consideration of potential baseline measures. 

This paper estimates the impact of known viruses and other determinants of health likely to increase the demand for healthcare in Wales across the 2025 to 2026 winter period. It should be used as an indication of what we expect to see based on historical data, rather than what will happen. A similar modelling approach has been taken for the past 3 years (2022 to 2023, 2023 to 2024 and 2024 to 2025). This 2025 to 2026 winter modelling report has also included additional statistical and mathematical modelling techniques which are stated throughout the report (and explained in further detail in the Appendix). 

This summer has seen higher-than-usual temperatures with provisional data suggesting summer 2025 has been the warmest summer on record for the UK. The impact of this year’s dry hot summer and the future impact of hotter dryer summers and warmer wetter winters is difficult to quantify, and this has not been taken into consideration.