Recent human metapneumovirus genomic diversity within expected evolutionary trends

In December 2024, human metapneumovirus (hMPV) gained international attention due to concerns over increases in cases in Chinese hospitals, leading the World Health Organization (WHO) to issue a statement indicating case numbers were within expected ranges. To assess potential variant emergence, 99 hMPV genomes, including 13 recent cases from November 2024 to January 2025, were sequenced from symptomatic patients in western Washington State. Phylogenetic analysis identified co-circulating sublineages, with A2b2 (containing a 111 nt duplication in the attachment glycoprotein G) being the most prevalent. Recent hMPV genomes did not form a single monophyletic group, indicating ongoing introductions and diverse variant circulation within sublineages. hMPV sublineages exhibit strong temporal signal and similar evolutionary rates, and particularly the faster-evolving A2b2-111dup lineage (1.1 × 10□ ³ substitutions/site/year), but no evolutionary features of heightened concern were detected. hMPV seasonal circulation and continuous evolution should be monitored closely, especially as vaccine trials are underway.