What question did this study set out to answer?

This study aims to evaluate mutations in the antigenic sites A-E of the hemagglutinin of A(H3N2) viruses in Brazil from 2025 to 2026.

May 15, 20260 citationsOpen Access

Antigenic features of Influenza A (H3N2) circulating in Brazil during 2025 and comparison with vaccine strains

IRIvan Ramos PGPriscila Gonçalves ADAnna Deodato

Key Points

This study aims to evaluate mutations in the antigenic sites A-E of the hemagglutinin of A(H3N2) viruses in Brazil from 2025 to 2026.
Complete HA sequences of A(H3N2) viruses and vaccine strains were obtained from the EpiFlu database.
Sequences were aligned and converted into amino acids to analyze localized changes in antigenic sites.
The study documented changes in 1,620 HA sequences and identified 6 subclades with relevant substitutions.
Identified antigenic mutations in site A (T135K, S144N, N145S) and site B (N158D, I160K, Q173R) in subclade K.
Some mutations are absent in the 2026 Southern Hemisphere vaccine strain but included in the Northern Hemisphere 2026/2027 strain.
The findings indicate potential antigenic drift which may affect vaccine effectiveness.

Abstract

Introduction: Genomic and phenotypic surveillance of the Influenza A(H3N2) virus is essential to monitor viral evolution and support decisions related to vaccine composition.Objectives: This study evaluated mutations in the antigenic sites A-E of the hemagglutinin (HA) of A(H3N2) viruses detected in Brazil between January 2025 and January 2026. Methodology:Complete HA sequences of the Influenza A(H3N2) virus and the three vaccine strains recommended by the WHO during the study period were obtained from the EpiFlu database (GISAID).The sequences were aligned and converted into amino acids to evaluate localized changes in the A-E antigenic sites, with emphasis on the A and B sites, which are historically associated with a greater antigenic impact. Results:The results revealed 1,620 A(H3N2) HA sequences recovered from Brazil, detecting 6 subclades (J.2, J.2.2, J.2.3, J.2.4, J.2.5, K) with multiple relevant substitutions in the antigenic sites.The transition from subclade J.2 to J.2.3 (EW12 to EW23) was observed, followed by the rapid emergence of subclade K (EW44/2025 to EW04/2026).We identified the fixation of mutations in antigenic site A (T135K, S144N, and N145S) and site B (N158D, I160K, and Q173R) within subclade K, some of these alterations (S144N, N158D, I160K, and Q173R) are not present in the A/Singapore/GP20238/2024 vaccine strain chosen for the 2026 Southern Hemisphere vaccine, however, the A/Darwin/1454/2025 strain selected for the Northern Hemisphere 2026/2027 season already includes these substitutions.This suggests a potential antigenic drift and reinforces the need for phenotypic testing to better characterize the circulating viruses.Additional alterations in sites C, D, and E were documented, although less frequently in isolated samples, contributing to the structural diversity of the glycoprotein. Conclusion:The comparative analysis indicates that the observed genetic diversity may influence vaccine effectiveness, requiring confirmation through antigenic analyses.This work reinforces the importance of integrated molecular surveillance to guide public health responses and future vaccine update.

KI fragen

Bookmark

View Full Paper