When scientists at St. Jude Children's Research Hospital first detected a novel strain of H5N1 avian influenza in late 2024, they didn't just flag it and move on. They mobilized a continental network of researchers to watch where it went — and what they learned is already helping protect people.
An international team led by St. Jude tracked the D1.1 strain as it emerged in Alaska and British Columbia and spread south and east across North America through migratory bird pathways. By coordinating with institutions across Canada and the United States, the researchers assembled the most comprehensive map yet of how this dominant strain moved through wild bird populations. Their findings, published in Nature Medicine, offer both reassurance and a blueprint for future surveillance.
"We've shown the value of connecting what are usually regional findings into a single comprehensive map to understand the strain's spread," said Richard Webby, Ph.D., corresponding author and researcher in St. Jude's Department of Host-Microbe Interactions. "That lets us put human cases in the context of the strain's greater spread and gives us a model to continue to monitor and assess the threat of these highly pathogenic influenza viruses in the future."
The timing of the study proved critical. Starting in 2024, severe human infections from avian influenza were reported across North America, and every severe case stemmed from the D1.1 strain. Initially, the geographic scatter of those infections seemed random. The new map revealed otherwise.
"We could connect all the severe cases with the wild bird map," said co-first author Walter Harrington, Ph.D. "Without that context, the human infections appeared geographically scattered; with it, the strain's emergence correlated with where we saw it becoming the dominant strain in wild birds."
Crucially, the researchers found that current human vaccine stockpiles are likely to work well against the D1.1 strain. Testing showed significant cross-reactivity with existing candidate vaccines, suggesting they could effectively help control the virus if needed. The team also classified the virus as low risk for human-to-human transmission in its current form.
"Fortunately, we saw that these viruses remained mostly avian, with none of the major mutations known to enable efficient human infections," said co-first author Lisa Kercher, Ph.D. The team did note the strain carries a mutation conferring resistance to a common antiviral — a finding that underscores the importance of ongoing monitoring.
The researchers emphasize that while the immediate risk to the general population appears low, the severity of individual infections serves as a reminder that vigilance matters. By joining forces across borders, they've built a model for tracking threats before they become crises.