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Updated: Feb 21, 2026
An Optimized Hemagglutination Inhibition HI Assay to Quantify Influenza-specific Antibody Titers
Published on: December 1, 2017
Modest protection from vaccination against influenza A(H3N2) subclade K, Beijing, China, 2025/26 season
Ying Shen1,2,3, Daitao Zhang1,2,4,3, Zhaomin Feng1,2,4,3
1Beijing Key Laboratory of Surveillance, Early Warning and Pathogen Research on Emerging Infectious Diseases, Beijing Center for Disease Prevention and Control, Beijing, China.
Abstract:
During the early 2025/26 influenza season, influenza A(H3N2) subclade K rapidly predominated in Beijing, China. Using a test-negative design, we estimated influenza vaccine effectiveness (VE) among influenza-like illness outpatients tested between weeks 40/2025 and 04/2026. Among 10,484 participants, sequencing of 316 randomly selected A(H3N2)-positive samples showed 84.8% were subclade K, and antigenic analysis of 65 viruses indicated antigenic divergence. Despite this, adjusted VE against laboratory-confirmed influenza was 23.5% (95% confidence interval: 11.7-33.7), indicating modest protection during this subclade K-dominated season.
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