Current flu vaccine provides moderate protection against severe disease, interim analyses suggest

Interim analyses from France and China report moderate vaccine effectiveness in early 2025–26—about 36% in the French dataset and about 41% in the Beijing dataset—with higher effectiveness in children and lower effectiveness in older adults.

Two interim analyses published in Eurosurveillance report that the 2025–26 seasonal influenza vaccine provided moderate protection during the early months of the season. Researchers in France and China analyzed national laboratory testing and viral sequencing as A(H3N2) subclade K strains spread. Both studies found measurable vaccine effectiveness against confirmed influenza, with stronger protection in children and weaker protection in older adults. Influenza activity began earlier and intensified faster this season compared with 2024–25. Main findings: - France: Analysis of 24,267 patients tested from November 2025 to January 2026 found 5,451 (22.5%) influenza-positive cases and an overall vaccine effectiveness (VE) of 36.4% against confirmed influenza. - France (age groups): VE was 57.2% for ages 0–17, 45.1% for ages 18–64, and 27.7% for ages 65 and older. - France (timing and strains): Influenza activity rose earlier than last season; early weeks were dominated by A(H1N1)pdm09 subclade D.3.1.1, with A(H3N2) subclade K increasing from week 49. Of >500 samples through week 50, 54.2% were H1N1 and 44.9% were H3N2, with K the most detected subclade. - China (Beijing): Among 9,579 patients tested from September to December 2025, 1,942 (20.3%) were influenza-positive, nearly all H3N2; sequencing of 316 samples found 84.8% of H3N2 belonged to subclade K. Overall VE was 41.3% and VE against H3N2 was 39.9%. - China (age groups and transmission): VE was 70.9% for children 5 and younger, 53.1% for ages 6–17, 25.3% for ages 18–59, and 25.3% for adults 60 and older; school-aged children made up an unusually large share of cases and subclade K was noted as highly transmissible. Summary: The two interim studies indicate the 2025–26 influenza vaccine provided moderate protection against confirmed cases during the early season, despite a mismatch with the circulating H3N2 subclade K. Both research teams reported age-related differences in effectiveness and noted that vaccination remained effective even with antigenic drift. The investigators recommended reinforcing vaccination uptake while influenza circulation continues.