Researchers are clarifying the transmission pathways and virus reservoirs that continue to move HPAI into commercial poultry. USDA officials said poultry vaccination remains in development, but unresolved strain coverage and trade concerns continue to limit deployment. New California dairy research found infectious H5N1 in milking parlor air and wastewater, while Wisconsin’s composting complaints show how HPAI's impacts extend beyond the poultry industry.
What’s Driving HPAI Transmission in Commercial Poultry?
More than three years into the current HPAI outbreak, researchers are focusing on the mix of factors that continue to move the virus into commercial poultry. Erica Spackman, acting research leader at the United States Department of Agriculture’s National Poultry Research Center, said the current clade 2.3.4.4b strain has “different biology than some of the previous HPAI or low-path AIs” the industry has faced. Current isolates require a dose roughly 1,000 times smaller to infect chickens and turkeys than 2014–2015 strains, with some isolates proving 10,000 times more infectious.
Spackman identified dabbling ducks, including mallards, as the central reservoir. “Dabbling ducks or puddle ducks are the main carriers and natural host species that become infected but don’t become sick,” she said. H5N1 can also persist in surface water for months, making ponds, drainage ditches, and runoff areas near poultry farms potential environmental reservoirs. Researchers are also studying whether rodents, skunks, raccoons, sparrows, starlings, and house flies may act as mechanical vectors between wild bird habitats and poultry facilities.
Dairy cattle have added a new transmission concern. “No one had this on their avian influenza bingo card,” Spackman said, noting that HPAI in cows was unexpected. Infected cows can shed extremely high levels of virus in milk, and some poultry infections have been genetically linked to nearby dairy operations where waste milk was land-applied. For producers, the implication is direct: HPAI control now depends on managing surface water, pests, wildlife access, nearby livestock risk, and traffic patterns alongside traditional barn-level biosecurity (Doughman, 2026).
USDA Says Poultry HPAI Vaccine Remains in Development
United States Department of Agriculture Secretary Brooke Rollins said an avian influenza vaccine is still in development during April 22 testimony before the Senate Appropriations Subcommittee on Agriculture, Rural Development, Food and Related Agencies. Rollins cited unresolved questions around vaccine performance across multiple strains and the potential impact on poultry trade, since some export markets restrict imports from countries that vaccinate flocks. During the hearing, Rollins said, “we don’t have all the data and I am not willing to put America up on the experimental block to lead the rest of the world on this.” (Rev.com, 2026) Rollins said USDA has spent $100 million on innovation, with roughly 80% directed toward vaccine research and potential pilot projects. For now, USDA is continuing to prioritize biosecurity and rapid response while vaccine work advances, reflecting the trade and implementation challenges that continue to shape U.S. poultry vaccination policy (Allen, 2026).
Study Finds Airborne and Wastewater H5N1 on California Dairy Farms
A PLOS Biology study published May 5 found evidence of infectious H5N1 in milking parlor air and wastewater on infected California dairy farms, pointing to possible transmission routes beyond direct cow-to-cow contact. Researchers sampled 14 H5N1-positive dairy farms in California during 2024 and 2025 and detected viral RNA in air, wastewater, cows’ exhaled breath, and milk. In expanded surveillance, H5N1 viral RNA was detected in 21 of 35 air samples, with infectious virus found in four. Viral RNA was also found across wastewater streams, including manure lagoons used by migratory birds and fields with grazing cows. Researchers identified enclosed milking parlors as a key exposure point for dairy workers because aerosolized milk may carry infectious virus (Van Beusekom, 2026).
USDA Funds Early-Stage Georgia Tech Oral Bird Flu Vaccine Project
The United States Department of Agriculture awarded $2 million to Georgia Tech and Georgia Tech Research Institute researchers for an early-stage project to develop an oral H5N1 vaccine for poultry that could be delivered through feed instead of individual injections. The project aims to use probiotic bacteria to design vaccine candidates that help chickens build immunity against avian influenza. If successful, the approach could make flock-level vaccination easier to administer in large poultry operations. The award comes as USDA officials continue to evaluate vaccine pilot projects while citing unresolved questions around efficacy, strain coverage, and trade impacts (Georgia Tech News Center, 2026).
Wisconsin and USDA Reduce Dairy H5N1 Testing Requirements
Federal and Wisconsin officials are scaling back H5N1 surveillance requirements for dairy cattle after a decline in detected infections over the past year. The USDA recently removed mandatory pre-movement testing for lactating dairy cows traveling between states classified as “unaffected” under the National Milk Testing Strategy, including Wisconsin and 41 other states. Wisconsin also rescinded its order requiring testing before cows could attend fairs and exhibitions and reduced statewide herd surveillance from monthly to every other month. Wisconsin has recorded only one confirmed dairy herd infection since H5N1 entered U.S. cattle in 2024, compared to broader spread in states like California and Idaho (United States Department of Agriculture, n.d.). However, some veterinary and laboratory officials expressed concern that the reduction in testing may reflect staffing and funding pressures at the USDA rather than reduced long-term risk, particularly as migratory wild birds continue to circulate the virus (Kirwan, 2026).
France Reports New H5N1 Farm Outbreaks After Easing Controls
France reported two new highly pathogenic avian influenza H5N1 outbreaks on farms in the southwest, just days after lowering its national bird flu risk level. According to the World Organisation for Animal Health, the virus was detected in chickens and vaccinated ducks, causing 270 deaths across premises with 5,062 birds. The remaining birds were culled as a precaution. The detections are notable because France had recently eased restrictions after citing improvements in farm and wild bird conditions. France began vaccinating ducks in 2023 after repeated severe H5N1 waves, but the latest cases show that vaccination reduces transmission risk without fully preventing infection (Global Ag Media, 2026).
Wisconsin Composting Complaints Highlight Disposal Burdens After Mass Depopulation
Palmyra, Wisconsin residents are raising odor concerns near an avian flu composting site tied to Daybreak Foods operations, underscoring the downstream management burden producers face after mass depopulation. According to the United States Department of Agriculture, two commercial flocks and one backyard flock in Wisconsin were depopulated in late February and March, totaling approximately three million birds. Since 2022, Wisconsin has lost 24 commercial flocks and 24 backyard flocks, accounting for more than 11 million birds statewide. The Wisconsin Department of Agriculture, Trade and Consumer Protection said the farm and contractor have complied with state and federal requirements for virus inactivation, while local officials said the process falls outside town regulatory authority. Daybreak Foods and the Wisconsin Department of Natural Resources have agreed to implement odor mitigation at the compost site (Bruner, 2026).
References
Allen, G. (2026, April 27). USDA Says Avian Influenza Vaccine Still in Development. Hoosier Ag Today. https://www.hoosieragtoday.com/2026/04/27/usda-says-avian-influenza-vaccine-still-in-development/
Bruner, A. (2026). Foul smell coming from avian flu composting site. Spectrumnews1.com. https://spectrumnews1.com/wi/milwaukee/news/2026/04/27/palmyra--birds--smell--dnr
Doughman, E. (2026, May 7). What’s driving HPAI transmission in commercial poultry. WATTPoultry.com. https://www.wattagnet.com/poultry-meat/diseases-health/avian-influenza/news/15824559/whats-driving-hpai-transmission-in-commercial-poultry
Georgia Tech News Center. (2026). Georgia Tech Bird Flu Vaccine Project Lands $2M From USDA | News Center. Georgia Tech News Center. https://news.gatech.edu/news/2026/04/28/georgia-tech-bird-flu-vaccine-project-lands-2m-usda
Global Ag Media. (2026). France reports new bird flu cases after easing controls. Thepoultrysite.com. https://www.thepoultrysite.com/news/2026/05/france-reports-new-bird-flu-cases-after-easing-controls
Kirwan, H. (2026, May 7). Federal, state officials relax testing for avian flu on dairy farms. WPR. https://www.wpr.org/news/federal-state-officials-relax-testing-avian-flu-dairy-farms
Rev.com. (2026). Brooke Rollins USDA Budget Testimony | Rev. Rev.com. https://www.rev.com/transcripts/usda-budget-hearing
United States Department of Agriculture. (n.d.). HPAI Confirmed Cases in Livestock | Animal and Plant Health Inspection Service. Www.aphis.usda.gov. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/hpai-confirmed-cases-livestock
Van Beusekom, M. (2026, May 5). Center for Infectious Disease Research and Policy. Umn.edu. https://www.cidrap.umn.edu/avian-influenza-bird-flu/sampling-reveals-possible-novel-sources-h5n1-avian-flu-transmission-dairy