- Researchers mapped the spread of the dominant D1.1 H5N1 strain across North American wild bird populations
- Findings link geographic spread in birds to reported human infections in 2024
- Study suggests low current risk of human-to-human transmission
- Existing vaccine stockpiles show likely effectiveness against the strain
- Collaboration across U.S. and Canada enabled a continent-wide surveillance model
An international team of scientists has produced the most comprehensive map to date of how a dominant strain of highly pathogenic avian influenza (H5N1) spread through wild bird populations across North America, providing new clarity on transmission pathways and associated human infection risks.
Led by researchers at St. Jude Children’s Research Hospital, the study—published in Nature Medicine—analyzed samples collected and sequenced from birds across the continent in 2024. The effort enabled scientists to track the emergence and movement of the D1.1 strain, now dominant in multiple regions.
Tracking the spread across migratory pathways
The research shows that the D1.1 strain first appeared in Alaska and British Columbia before spreading southward and eastward along established migratory bird routes. By integrating surveillance data from multiple institutions across the United States and Canada, the team constructed a continent-wide view of viral transmission.
This coordinated approach allowed researchers to connect what were previously isolated regional observations into a unified understanding of how the virus disseminated through wild bird populations.
Linking animal spread to human cases
The study also helps explain the geographic distribution of severe human infections reported in 2024. All such cases were linked to the D1.1 strain, though prior to this analysis, their scattered locations made patterns difficult to interpret.
By overlaying human infection data with the avian spread map, researchers identified a clear correlation between areas where the strain became dominant in birds and where human cases emerged.
Assessing human health risk
Despite its widespread presence in birds, the D1.1 strain currently appears to pose limited risk for sustained human transmission. Researchers found that the virus remains largely adapted to avian hosts and lacks key mutations associated with efficient human-to-human spread.
However, the virus does carry a mutation conferring resistance to a commonly used antiviral drug. Encouragingly, testing of existing candidate vaccines demonstrated strong cross-reactivity, suggesting current stockpiles would likely be effective if needed.
While overall public health risk is considered low at present, researchers emphasized that the severity of illness in confirmed human cases underscores the importance of continued surveillance and preparedness.
A model for future surveillance
The study highlights the value of international collaboration in tracking emerging infectious diseases. By combining datasets across borders and disciplines, researchers were able to contextualize both animal and human infections within a single framework.
This approach may serve as a model for monitoring future outbreaks of highly pathogenic influenza and other zoonotic diseases with pandemic potential.
Information sourced from a press release issued by St. Jude Children’s Research Hospital.
