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Abstract

INTRODUCTION

There remains uncertainty whether global influenza seasonality, viral dynamics and epidemic duration have re-established after 2021.

AIM

We describe global circulation patterns of influenza viruses from 2021 to 2025 and discuss implications for prevention and surveillance.

METHODS

We analysed World Health Organization (WHO) FluNet sentinel and non-sentinel/not-defined virological data from week 1/2021 to 26/2025, stratifying by latitude, region and season. We calculated influenza positivity rate, proportion of virus (sub)types, typical peak timing and duration of influenza epidemics (applying the 75% annual average percentage method).

RESULTS

Sentinel surveillance in 120 countries reported 500,870 detections in this period; positivity rate rose globally from 3.0% in 2021 to 23.7% in 2024. Type A viruses caused over two-thirds of cases, with variability across WHO Regions and seasons. Among A subtypes, A(H3N2) dominated in 2021/22 and A(H1N1)pdm09 in 2023/24, while all but three influenza B cases were B/Victoria. Epidemic peaks typically occurred from December to March and May to August in northern and southern hemispheres countries, respectively, while tropical countries showed highly heterogeneous timing. The median epidemic duration was ca 10 weeks above 30° north, and it varied between 15 and 30 weeks at more southern latitudes. Non-sentinel/not-defined feeds showed stronger A-skew and lower characterisation.

CONCLUSION

Influenza virus circulation shows convergence toward seasonal architectures described before the COVID-19 pandemic, although changes in lineage ecology and epidemic duration persist. Our results confirm the need for latitude-tailored vaccination schedules, consolidation of trivalent vaccines, and strengthened surveillance to better anticipate changes in influenza circulation and support preparedness.

© Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
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/content/10.2807/1560-7917.ES.2026.31.21.2500743
2026-05-28
2026-06-10
/content/10.2807/1560-7917.ES.2026.31.21.2500743
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Global influenza epidemiology after 2020: patterns of circulation, epidemic timing and duration, and implications for vaccination strategies
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Marco+Del+Riccio&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Del Riccio Marco</a>, <a href="/search?value1=Saverio+Caini&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Caini Saverio</a></span>. Global influenza epidemiology after 2020: patterns of circulation, epidemic timing and duration, and implications for vaccination strategies. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(21):pii=2500743. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.21.2500743" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.21.2500743</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 21 Sept 2025;&nbsp;&nbsp; <span class="generated">Accepted</span>: 22 Jan 2026 </span> </p>
/content/10.2807/1560-7917.ES.2026.31.21.2500743
/content/10.2807/1560-7917.ES.2026.31.21.2500743
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