Trait-based ViTAP assessment of pandemic potential for US avian influenza A (H5N1) clade 2.3.4.4b.

Highly pathogenic avian influenza A (H5N1) clade 2.3.4.4b is now widespread in US birds and has spilled over into mammals, raising concern about pandemic emergence. We applied the Viral Trait Assessment for Pandemics (ViTAP) model to score 11 intrinsic viral traits using a structured literature review, expert elicitation, and sensitivity analyses. The resulting composite score for contemporary US H5N1 was 3.28/5 (moderate-high risk); transmission-related traits contributed most to score uncertainty, while the absence of sustained human-human spread currently limits risk. Thus, ViTAP provides a transparent way to prioritize surveillance, countermeasure development, and preparedness as H5N1 continues to evolve.