Emergence and Global Circulation of the HRSV BA Variant with a 7-AA Extension in the G Protein Under Persistent BA Predominance - Global, 1996-2025.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: Human respiratory syncytial virus variant with a 7-amino-acid extension in the G protein of the BA genotype (BA-7AA) is associated with severe neonatal pneumonia outbreak, high intensive care unit occupancy and death. However, limited data are available on the epidemiology and transmission dynamics of the BA-7AA variants. WHAT IS ADDED BY THIS REPORT?: This study integrated publicly available sequences of the second hypervariable region of the G gene of the BA-7AA variant with those sequenced in this study to clarify the emergence and transmission dynamics of the BA-7AA variant. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: By revealing the circulation of the BA-7AA variant, this study established a basis for forecasting and warning of the reemergence of BA-7AA variants associated with severe cases and outbreaks.