{
  "id": 12526698,
  "title": "The mammalian-adaptive PB2-E627K substitution preserves viral fitness of clade 2.3.4.4b H5N1 HPAIV in birds.",
  "url": "https://urgent.news/2026/10/06/the-mammalian-adaptive-pb2-e627k-substitution-preserves-viral-fitness",
  "topic": "science",
  "section": "Science",
  "published": "2026-10-06T00:00:00.000Z",
  "source": {
    "name": "bioRxiv",
    "slug": "biorxiv",
    "url": "https://www.biorxiv.org/content/10.64898/2026.10.06.757006v1?rss=1"
  },
  "original_language": "en",
  "account": "The clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) has spread worldwide since 2020, infecting wild birds and poultry and causing mass mortalities in some instances. Spill-over events into mammals can lead to mammalian-adaptive mutations that heighten the risk to humans. The most well-known of these is the glutamate to lysine change at position 627 in the polymerase basic 2 protein (PB2-627K). While PB2-627K enhances viral replication in mammalian cells, it is relatively uncommon in avian populations. This study examined how PB2-627K affects viral fitness in birds, aiming to gauge the likelihood of mammalian-adapted viruses re-establishing in avian species, similar to how PB2-627K has emerged in mammals after scavenging on them. The researchers used a representative H5N1 virus (European genotype AB) and discovered that PB2-627K boosted polymerase activity and replication in human cells without hindering replication in avian cells. An isolate from a fox with PB2-627K had replication rates and transmission efficiency in chickens and ducks comparable to a closely related PB2-627E virus. Of particular note, PB2-627K remained genetically stable following infection and transmission in both avian hosts. These findings indicate that mammalian-adaptive mutations acquired during spill-over can persist in avian populations, potentially increasing the risk of zoonotic transmission and highlighting the need for surveillance of such mutations in birds.",
  "summary": "Since emerging in 2020, clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) has disseminated globally, causing substantial infection and mortality in wild birds and poultry. Additionally, numerous spill-over events into mammals have occurred, including mass mortalities and sporadic human infections. Such events can drive the acquisition of mammalian-adaptive mutations, which…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}