H5N1 Update for June 2025
Authors: Ifrah Ahmad, Gregory Kirchoff
Previous update October 2024:
https://whn.global/newsletter/h5nhttps://whn.global/newsletter/h5n1-update/1-update/
Other WHN resources on H5N1:
https://whn.global/global-considerations-for-h5n1-risks-and-preparedness/
H5N1 avian influenza continues to spread globally in poultry and within cattle herds in the United States. Tracking the extent of this spread remains difficult, as testing has been limited or in some cases halted entirely. In early April, a child in Mexico died from H5N1, following similar deaths in Canada and the U.S. last year. All three cases involved the same strain: D1.1 (2.3.4.4b) [1,2].
In 2024, cattle herds were infected across the US, linked to detected and undetected infections in people [3,4]. At the end of 2024, there were early reports of H5N1 clade D1.1 (2.3.4.4b) infecting cattle, pointing to increased risk of further infections by the variant involved in deadly infections [5]. Recent structural analysis suggests that a single glutamine to leucine mutation within this variant would be sufficient to enable binding to human receptors [6]. Despite this development, there has been little follow-up on infections among livestock or farm workers—raising concerns about the adequacy of current surveillance efforts.
In response to the decline in testing and reporting, modeling efforts have been used to estimate outbreak risk across the U.S. states. According to one study [7], Arizona and Wisconsin face the highest risks of outbreaks emerging among dairy cows—yet neither has reported any confirmed cases. Arizona, with the largest mean herd size in the country, has extensive cattle trade ties with California and Texas that have reported many outbreaks. Wisconsin, further from the epicenter, has the largest number of dairy herds in the country with over 6200 herds.
The study adds to the growing evidence that significant underreporting is occurring and warns that dairy herd outbreaks will continue to be a significant public health challenge in 2025. Beyond the risk of further infections of people and viral adaptation for human transmission, the economic losses due to this virus’ effects on the US dairy sector are estimated to range from $14 billion to $164 billion [8]. The country’s over 9 million milk cows contribute approximately 3% of the nation’s GDP.
So far, the only federal rule requires testing lactating dairy cows before they’re moved across state lines. Even if the herd is larger, only up to 30 cows need to test negative for H5N1 for the shipment to go ahead. This kind of sampling makes it hard to miss a widespread outbreak—but it won’t catch every single case. Still, if even one of the tested cows is positive, the move is blocked and the entire herd must wait 30 days before retesting. Non-lactating cows, like dry cows and heifers, aren’t covered by the testing rule. There’s also no testing required for cows moved within a single state, and the test results aren’t currently shared with public health agencies.
Given the mounting health and economic risks, urgent action is needed to contain the spread of H5N1. In response, the Public Health Agency of Canada has purchased 500,000 doses of human H5N1 vaccine to mitigate the risk of human transmission [9]. The Global Virus Network (GVN), a coalition of leading virologists, has issued an urgent call to treat the outbreak as a serious threat with the potential to spark a global pandemic, calling for a far more coordinated response [10]. The UN Food and Agriculture Organization (FAO) has similarly emphasized the need for globally coordinated action to address the growing risk [11].
References
[1] https://apnews.com/article/mexico-bird-flu-h5n1-4c8a2bc81e565e2948e237c676094415
[2] https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON564
[3] Current Situation: Bird Flu in Dairy Cows | Bird Flu | CDC
[4] Many human infections with ‘cow flu’ are going undetected | Science | AAAS
[5] https://www.aphis.usda.gov/news/program-update/aphis-confirms-d11-genotype-dairy-cattle-nevada-0
[7] https://www.nature.com/articles/s41467-025-59554-z
[9] Canada buys 500,000 doses of H5N1 avian influenza vaccine for those most at risk | CBC News