Weekly Epidemiological Record, 2025, vol. 100, 13/14 [full issue]

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World Health Organization = Organisation mondiale de la Santé

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20 p
The development of influenza candidate vaccine viruses (CVVs), coordinated by WHO, is a key component of global influenza pandemic preparedness. This article summarizes the genetic and antigenic characteristics of zoonotic influenza A viruses detected between September 2024 and February 2025 and reviews the development and updating of CVVs to ensure their continued relevance as these viruses evolve. It provides an overview of recent human and animal detections, with particular attention to influenza A(H5) viruses, their geographic distribution, phylogenetic diversification and antigenic properties, and describes changes that may affect the suitability of existing candidate vaccine viruses. The article assesses genetic and antigenic data for circulating virus clades, compares newly detected viruses with available CVVs and identifies instances where additional or updated CVVs are warranted. It also summarizes the epidemiological context of zoonotic influenza infections in humans and animals and presents the status of available candidate vaccine viruses for multiple influenza A subtypes of pandemic concern. The document supports ongoing risk assessment and preparedness activities by informing vaccine development priorities and facilitating international collaboration in pandemic planning.
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