Emergence of SARS-CoV-2 omicron subvariant NB.1.8.1 in India: Genomic evolution, transmission patterns, and public health implications

Background and objectives The NB.1.8.1 Omicron subvariant has demonstrated notable epidemiological relevance in India, though without evidence of a marked increase in severity compared to prior Omicron waves. Understanding its genomic trajectory and policy implications is critical. Methods This was a retrospective convergent mixed-methods study integrating genomic sequencing (GISAID, INSACOG), epidemiological counts (ICMR, WHO, CDC), and policy/advisory analysis (MoHFW, WHO-SEARO). Data were analysed across January-May 2025 using prevalence tracking, hospitalisation comparisons, and thematic policy review. Results Genomic analyses showed NB.1.8.1 carrying lineage-defining spike mutations (A435S, V445H, T478I) linked to transmissibility and immune escape. While prevalence rose in China, India reported