Eurosurveillance - Volume 31, Issue 21, 28 May 2026

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

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

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).

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.

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.

Pneumococcal vaccination has been recommended in Germany for adults aged ≥ 60 years (1998) and children aged < 2 years (2006), resulting in a reduction of pneumococcal disease incidence in vaccinated children and unvaccinated individuals through herd protection.

We aimed to investigate serotype distribution of invasive pneumococcal disease (IPD) among children and adults in 2017–2024.

We analysed data of an ongoing nationwide surveillance of IPD. All isolates were serotyped by Neufeld’s Quellung reaction.

In total, 24,122 IPD isolates were analysed by the German Reference Laboratory for Streptococci. Over the study period, case numbers were lower during the COVID-19 pandemic and increased afterwards with higher proportion of pneumococcal conjugate vaccine (PCV)13 serotypes. Serotypes 22F and 33F, included in PCV15 and PCV20, showed only minor variations, whereas PCV20 unique serotypes were less frequently observed in 2022–2024. Serotype 3 persisted in IPD across all age groups, while serotype 4 disappeared in children and adolescents, but increased in adults, most prominently in 18–49-year-olds. Serotype 38 steeply increased in 2023/24, among children aged < 2 years and older adults.

The concerning increase of PCV13 serotype IPD in Germany might be related to low vaccination uptake, resulting in inefficient herd protection. The dominance of serotype 3 and the rise of serotype 4 among adults highlight the importance of direct protection and support the current national vaccination recommendation for adults aged ≥ 60 years. The increase in serotype 38 IPD among young children and older adults might indicate a replacement phenomenon, highlighting the importance of IPD serotype surveillance.