The flu season 2025–2026 is expected to remain intense across Europe, marked by high influenza activity, moderate vaccine effectiveness, and compounded pressure from other circulating respiratory pathogens. While vaccination may not prevent all infections, it remains essential for reducing severe disease, protecting high-risk populations, and maintaining healthcare system resilience across the EMEA region during the influenza season.
Overview of the 2025–2026 European Flu Season
The flu season 2025–2026 has started earlier than usual across the WHO European and EMEA regions, beginning approximately four weeks ahead of the historical average. While early onset is not unprecedented, surveillance data indicate a rapid and sustained rise in respiratory infections in Europe, particularly seasonal influenza, since late autumn. Multiple European countries are currently reporting high to very high influenza activity, with increasing positivity rates among sentinel respiratory samples. This escalation is already placing pressure on healthcare systems, especially affecting older adults, immunocompromised individuals, and patients with chronic conditions, who are traditionally at higher risk during the flu season. Importantly, influenza circulation is occurring alongside other seasonal viruses, including SARS-CoV-2 (COVID-19) and respiratory syncytial virus (RSV). This co-circulation of respiratory pathogens is a defining feature of the current European winter season and significantly contributes to the overall healthcare burden during the flu season 2025–2026.
Respiratory Infections in Europe: Virological Trends and Influenza Strain Dominance
A key characteristic of the flu season 2025–2026 in Europe is the dominance of influenza A(H3N2) viruses, specifically those belonging to subclade K. This subtype has rapidly become the most prevalent circulating influenza strain in several European countries. Influenza viruses are characterized by high mutation rates, driven by antigenic drift, which results in gradual genetic changes—especially in the hemagglutinin (HA) protein, the primary target of neutralizing antibodies. Genetic and antigenic analyses indicate that the currently circulating A(H3N2) subclade K viruses are antigenically distinct from the strains included in the 2025–2026 seasonal influenza vaccine formulation, resulting in partial vaccine mismatch. Despite this mismatch, there is no evidence of increased virulence or severity associated with this subclade. The current epidemiological impact appears to be driven primarily by higher transmissibility and immune escape, rather than increased pathogenicity. It is important to note that the number of mutations alone does not determine vaccine performance. Vaccine effectiveness depends on whether mutations occur in critical antigenic sites of the HA protein that influence immune recognition.
Seasonal Influenza Vaccines in Europe: Composition and Antigenic Match
Each year, the World Health Organization (WHO) issues recommendations for influenza vaccine composition for the Northern Hemisphere, based on global data from the Global Influenza Surveillance and Response System (GISRS). For the flu season 2025–2026, antigenically drifted A(H3N2) viruses emerged after vaccine strain selection. As a result, the match between circulating influenza viruses and the vaccine’s H3N2 component is suboptimal. This recurring challenge, particularly with H3N2 strains, reflects their faster evolution compared to other influenza subtypes during the influenza season in Europe.
Influenza Vaccine Effectiveness During the 2025–2026 Season
Preliminary data from European influenza surveillance networks estimate moderate influenza vaccine effectiveness, ranging from approximately 52% to 57% against laboratory-confirmed influenza A(H3N2) infections in outpatient settings. Crucially, even with reduced effectiveness against infection, seasonal flu vaccination remains highly effective at preventing severe outcomes during the flu season 2025–2026, including:
- Hospitalization
- Serious complications
- Influenza-related mortality
This protective effect is particularly significant for elderly populations, individuals with underlying medical conditions, pregnant women, and healthcare workers. A reduced level of protection against infection should not be misinterpreted as vaccine failure. Instead, it highlights the biological challenges posed by antigenic drift and underscores the role of vaccination as a core public health strategy to limit disease severity and healthcare system overload during the European flu season.
Public Health Impact of Seasonal Respiratory Diseases in EMEA
The current epidemiological pattern of the flu season 2025–2026 (early influenza onset, dominance of a drifted H3N2 strain, partial vaccine mismatch, and co-circulation of multiple respiratory viruses) is consistent with known influenza dynamics in Europe. These trends emphasize the importance of:
- Continuous virological surveillance
- Integrated respiratory virus monitoring
- Sustained seasonal vaccination strategies
Such measures are critical to reducing the burden of respiratory infections in Europe and guiding future vaccine strain selection.
Forecast for the European Winter Season
Based on current surveillance and virological data, projections for the flu season 2025–2026 include:
Continued Increase in Influenza Cases
The early start of the season and the high transmissibility of A(H3N2) subclade K suggest a continued rise in influenza cases over the next 6–8 weeks, with persistently high levels of respiratory illness across Europe.
Healthcare System Pressure
Although intrinsic severity has not increased, high infection volume may drive higher influenza hospitalization in Europe – particularly among vulnerable groups – intensifying healthcare system pressure.
Ongoing Role of Vaccination
Seasonal influenza vaccination remains the most effective intervention to reduce severe outcomes during the flu season 2025–2026, even when infection prevention is incomplete.
Interaction with Other Respiratory Viruses
The concurrent circulation of influenza, COVID-19, and RSV may result in overlapping peaks of respiratory illness, further increasing hospital occupancy and demand for healthcare services.
Public Health Recommendations
To mitigate the impact of the flu season 2025–2026, authorities recommend:
- Ongoing vaccination campaigns
- Enhanced surveillance of respiratory infections
- Preventive measures such as hand hygiene, mask use in crowded settings, and appropriate clinical management
Conclusions
As respiratory infections increase across Europe, health authorities emphasize the importance of seasonal flu vaccination and ongoing surveillance. Despite viral evolution and partial vaccine mismatch, immunization remains essential to limit hospitalizations and reduce the impact of the flu season 2025–2026 across the EMEA region.
References
- World Health Organization (WHO). Influenza season underway across the WHO European Region: WHO calls for vigilance and vaccination. WHO Regional Office for Europe, 2025.
- World Health Organization (WHO). Disease Outbreak News: Seasonal influenza update, 2025.
- European Centre for Disease Prevention and Control (ECDC). Influenza virus characterization and circulation in Europe, 2025.
- Petrova VN, Russell CA. The evolution of seasonal influenza viruses. Nature Reviews Microbiology. 2018;16:47–60.
- World Health Organization (WHO). Recommended composition of influenza virus vaccines for use in the 2025–2026 northern hemisphere influenza season. WHO, 2025.
- Belongia EA, McLean HQ. Influenza vaccine effectiveness: defining the H3N2 problem. Clinical Infectious Diseases. 2019;69(10):1817–1823.
- European Centre for Disease Prevention and Control (ECDC). Early estimates of seasonal influenza vaccine effectiveness in Europe, 2025.
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