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Updated: Jan 18, 2026

An Optimized Hemagglutination Inhibition HI Assay to Quantify Influenza-specific Antibody Titers
Published on: December 1, 2017
Interim vaccine effectiveness against influenza virus among outpatients, France, October 2025 to January 2026
Allan De Clercq1,2, François Blanquart3, Vincent Vieillefond4
1Hospices Civils de Lyon (HCL), Centre National de Référence des virus des infections respiratoires, Institut des Agents Infectieux, Laboratoire de Virologie, Lyon, France.
Abstract:
In Europe, the 2025/26 seasonal influenza epidemic started in October 2025. Co-circulation of A(H3N2) and A(H1N1)pdm09 was observed in several countries including France. We estimated early vaccine effectiveness (VE) against influenza virus in French outpatients (5,451 positives/18,816 negatives). A significant VE across all age groups was measured: 28% (95% CI: 17-37) for those aged ≥ 65 years, 45% (95% CI: 36-53) for 18-64-year-olds and 57% (95% CIs: 29-74) for 0-17-year-olds. Reinforcing vaccination uptake is warranted.
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