FDA Response to H5N1 Bird Flu in Dairy Cattle and Milk (2024)

Table of Contents

1. What the FDA Did, April to December 2024
2. Who Does What in the Federal Response
3. Viral Fragments Versus Live Virus: How the Tests Work
4. The First Retail Survey: 297 Samples (April–May 2024)
5. The June 2024 Letter to States on Raw Milk
6. The Research Agenda and the Pasteurization Study (June 2024)
7. The Second Retail Survey: 167 Samples (August 2024)
8. Industry Letters and the Silo Study (September–October 2024)
9. The December 2024 Raw-Milk Cheese Sampling Assignment
10. What the 2024 Actions Do Not Do
11. Dates and Status as of 11 October 2026
12. How the Response Fits the Federal-State Milk Safety System
13. Primary Documents
14. Key Research Papers
15. Connections

1. What the FDA Did, April to December 2024

The FDA’s response was a series of tests, studies and letters rather than a new rule. It was published as dated updates on one FDA web page, “Investigation of Avian Influenza A (H5N1) Virus in Dairy Cattle.” None of the 2024 steps was a Federal Register rulemaking, so none has a Federal Register docket number. The main steps, as that page and the linked FDA documents record them:

1. 25 April 2024: first results from a nationally representative survey of retail milk — about 1 in 5 samples carried viral fragments, with more positives from areas with infected herds.
2. 26 April, 1 May and 10 May 2024: follow-up testing of every fragment-positive sample found no live virus in any of the 297 retail samples; powdered infant formula and toddler formula tested negative for viral fragments; the FDA made an additional $8 million available for its milk-safety work.
3. 6 June 2024: a letter to state, territorial, local and tribal health partners on raw milk.
4. 25 June 2024: a published research agenda, and the launch of a second retail survey.
5. 28 June 2024: results of an FDA–U.S. Department of Agriculture (USDA) study that simulated commercial pasteurization.
6. 13 August 2024: second retail survey results — all 167 samples negative for live virus.
7. 26 September 2024: an update on FDA-funded research.
8. 30 September 2024: FDA–USDA letters to dairy processors and dairy retailers.
9. 3 October 2024: states invited into a blinded “silo study” of raw milk at processing plants, starting 28 October.
10. 23 December 2024: a regulatory sampling assignment for aged raw cow’s-milk cheese.

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2. Who Does What in the Federal Response

The FDA page describes the outbreak as one “impacting poultry, dairy cows, and people in multiple states,” investigated by the USDA, the FDA and the Centers for Disease Control and Prevention (CDC) together with state partners. It divides the work this way:

• FDA: “ensuring the safety of the milk, dairy products, and animal feed supply.” That is the subject of this page.
• USDA’s Animal and Plant Health Inspection Service: leads the response “from the animal health perspective” — the health of the herds themselves.
• CDC: works with both; the FDA page points readers to CDC for human surveillance.

The laboratory work in the FDA’s retail surveys was done by USDA scientists: the FDA reports that a USDA Agricultural Research Service laboratory analyzed the samples, and the silo-study samples went to USDA’s National Veterinary Services Laboratory. Herd testing, rules on moving cattle and counts of human cases are USDA and CDC matters and are not reported on this page.

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3. Viral Fragments Versus Live Virus: How the Tests Work

The FDA’s results make sense only once two kinds of test are told apart. The agency’s “Data Considerations” section explains them:

• qRT-PCR (quantitative reverse-transcription polymerase chain reaction) is a screening test that detects the virus’s genetic material. A positive result means genetic material was found, but, in the FDA’s words, “that does not mean that the sample contains an intact, infectious pathogen,” because the test also picks up leftover genetic material from virus already killed by heat such as pasteurization.
• Embryonated egg viability testing — injecting a sample into a fertilized chicken egg and watching whether virus multiplies — is described by the FDA as the “gold standard” for detecting live, infectious virus. It is the most sensitive method but slower.
• MDCK cell culture (Madin-Darby canine kidney cells) is a faster test for live virus, but the FDA notes it is less sensitive and may give false negatives when very little virus is present.

In every retail survey the FDA screened samples by PCR first and then ran live-virus tests on the PCR-positive ones. A sample that was PCR-negative needed no further testing.

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4. The First Retail Survey: 297 Samples (April–May 2024)

FDA milk specialists collected 297 samples of retail dairy products in 17 states between 18 and 22 April 2024. Because milk from many farms is pooled, pasteurized in one state and sold in another, the FDA recorded where each product was processed: the samples came from 132 processing locations in 38 states. The products were skim, 1%, 2% and whole milk, cottage cheese, cream, half and half, sour cream and similar products, and yogurt.

• 25 April: the FDA reported that about 1 in 5 samples tested so far were PCR-positive for viral fragments, “with a greater proportion of positive results coming from milk in areas with infected herds,” and repeated that a PCR-positive result does not by itself show live virus.
• Final tally (10 May): 60 of the 297 samples (20.2%) were PCR-positive; egg-inoculation testing of all 60 found no live virus (0 of 60). The FDA said these confirmatory results “mark the completion” of its laboratory work on the 297 samples.
• Infant and toddler formula: samples of retail powdered infant formula and powdered milk products marketed as toddler formula were all PCR-negative, so no further testing was needed.
• Funding: on 10 May the FDA announced an additional $8 million for its response — to validate pasteurization criteria, carry out surveillance at different points in the milk system, add laboratory capacity and train staff in biosecurity, and to support state partners and possible university research.

The FDA stressed that this survey “was designed to assess the effectiveness of the PMO milk safety system; it was not designed to assess the prevalence of H5N1 in dairy herds,” and that the samples “represent a snapshot in time.” Its 1 May update also stated that the FDA “continues to advise strongly against the consumption of raw milk and recommends that industry does not manufacture or sell raw milk or raw milk products.”

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5. The June 2024 Letter to States on Raw Milk

On 6 June 2024 the FDA sent a letter to state, territorial, local and tribal health partners, signed by its agency incident coordinator, then the acting director of its Center for Food Safety and Applied Nutrition. It set out the legal position and the agency’s concern:

• The legal split: selling raw milk for people to drink across state lines (“interstate commerce”) is prohibited under FDA authority, citing the federal regulation 21 CFR 1240.61. Sales within a state (“intrastate”) are a matter for each state, and the FDA noted that a number of states permit them, under varying rules.
• The science: the letter states that infected cattle shed the virus in their milk, so “all raw milk produced from herds with HPAI H5N1 infections has the potential to contain infectious HPAI H5N1 virus,” making raw milk “a potential route of consumer exposure.”
• The unknown: “Based on the limited research and information available, we do not know at this time if the HPAI H5N1 virus can be transmitted to humans through consumption of raw milk and products made from raw milk from infected cows.” The letter added that exposures on affected farms had been associated with three documented cases of H5N1 illness in dairy workers.

The letter’s recommendations to states were to tell the public about the health risks of raw milk; to monitor herds for signs of infection, with milk from sick cows discarded and raw milk fed to calves or other animals heat-treated or pasteurized; to run surveillance testing of herds that supply raw milk for sale in the state, with FDA technical help on request; and, in states that allow raw-milk sales, to use their authorities “to stop the sale of raw milk that may present a risk to consumers,” for example within a defined area. On its web page the FDA restated its long-standing position that raw milk “is considered a high-risk food because it has the potential to be contaminated with pathogens that cause illness and it has been linked to numerous foodborne illness outbreaks in the past.” These are the FDA’s statements and recommendations to states; they did not change any state’s law.

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6. The Research Agenda and the Pasteurization Study (June 2024)

On 25 June 2024 the FDA published a research agenda (dated 24 June) with three objectives: understand how heat and other methods inactivate H5N1 in dairy products (including bench-top heat studies, continuous-flow pasteurization studies, and the survival of the virus in raw-milk cheese during aging); determine the safety of retail dairy products; and develop “One Health” interventions — ways to prevent or control the virus across animals, milk and the environment, including the disposal of discarded milk.

On 28 June the FDA and USDA announced the results of what the FDA called “the only one to date designed to simulate commercial milk processing”:

• How much virus raw milk carries: researchers tested 275 raw milk samples from multiple farms in four affected states, deliberately chosen from regions with infected herds (so not nationally representative). 158 were positive for viral fragments; 39 contained infectious virus, at an average of 3.5 log₁₀ egg infectious doses (EID₅₀) per millilitre — about 3,000 virus particles per millilitre.
• The test: raw whole milk was spiked with far more virus than any raw sample contained — about 6.7 log₁₀ EID₅₀ per millilitre, roughly 5 million particles — and run through continuous-flow equipment at 161°F (72°C) for 15 seconds, the “high-temperature short-time” (HTST) or “flash” pasteurization most used by the dairy industry.
• The result: in each of nine repeated experiments the virus was completely inactivated. From samples taken mid-process, FDA engineers extrapolated that HTST conditions likely eliminate at least 12 log₁₀ EID₅₀ per millilitre (about 1 trillion particles), which the FDA described as “a large margin of safety.”

An FDA consumer safety officer contrasted the study with “some recent benchtop studies published by other institutions which have shown mixed results regarding the sensitivity of the virus to thermal treatment,” saying those relied on equipment “likely not sufficient to accurately simulate” commercial HTST conditions. The study was later published in the Journal of Food Protection (paper 1 below).

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7. The Second Retail Survey: 167 Samples (August 2024)

The second survey, launched in late June, was meant to fill geographic and product gaps left by the first, including states not covered earlier. On 13 August 2024 the FDA announced the results:

• 167 samples of aged raw-milk cheese, pasteurized fluid milk and products made from pasteurized milk (cheeses, cream cheese, butter and ice cream) were analyzed by a USDA Agricultural Research Service laboratory between 18 June and 31 July 2024.
• The samples were collected by a third party and repackaged to remove identifying marks before testing.
• 29 samples (17.4%) were PCR-positive for viral RNA; none of the 167 contained live virus. All 23 samples of aged raw-milk cheese were PCR-negative.

The FDA said the results “strengthen previous assessments that commercial pasteurization inactivates the H5N1 virus.” On 26 September the agency added a research update listing FDA-funded work with university and federal partners: heat-inactivation studies at time and temperature combinations outside standard pasteurization, studies of H5N1 under different aged raw-milk cheese processes, live-virus testing capacity, practical disposal of raw milk waste, and genome-edited chickens less susceptible to H5N1.

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8. Industry Letters and the Silo Study (September–October 2024)

On 30 September 2024 the FDA’s Deputy Commissioner for Human Foods and a USDA Deputy Under Secretary co-signed two letters, one to the dairy processing industry and one to dairy retailers. The letters:

• state that the FDA first assessed the commercial pasteurized milk supply as safe in late March 2024, based on existing science, pasteurization’s record against other pathogens and an egg-products study, and then confirmed that assessment through “three pivotal studies” — the 297-sample survey, the HTST study and the 167-sample survey;
• note the agencies’ awareness of concerns that processors might reject milk from farms identified as having, or possibly having, infected herds — a concern that could discourage farms from joining voluntary testing programs;
• encourage participation in USDA’s voluntary Dairy Herd Status Program and other voluntary monitoring studies; and
• note that cows can shed virus before or without symptoms, so raw milk bound for processing “might not be free of virus,” while stating that HTST pasteurization fully inactivated the levels of live virus found in raw milk.

On 3 October the FDA announced that states had been invited into “the silo study.” Beginning 28 October 2024, Grade “A” raw cow’s milk intended for pasteurization would be sampled from storage silos at dairy processing plants in participating states over six weeks. The study was double-blinded and “designed for data-gathering purposes only, with no intent or means of traceback or trace forward”; no participating state or facility would be identified. State participation was voluntary, samples went to USDA’s National Veterinary Services Laboratory, and the FDA, USDA and the National Conference on Interstate Milk Shipments said they would review the results.

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9. The December 2024 Raw-Milk Cheese Sampling Assignment

The last 2024 step, dated 23 December, differed from the earlier surveys. The FDA describes its research as research, but this assignment as “a regulatory activity.” In the United States, the FDA notes, cheese allowed to be made from raw milk must be aged for at least 60 days to reduce the risk from any pathogens. The assignment page (current as of 30 December 2024) sets out the plan:

• What: 300 samples of raw cow’s-milk cheese aged at least 60 days, with label information.
• Where: warehouses and distribution hubs across the United States — not retail stores — with no more than five samples per site.
• When: collection from as early as the end of December, expected to finish by the end of March 2025.
• How: PCR screening first, then a USDA-developed egg-inoculation test for live virus on PCR-positive samples.
• Follow-up: the FDA said it would not require any action from a firm on a PCR-positive result alone; if live virus were confirmed, it would decide case by case and might take steps “such as a recall, follow-up inspection, or other possible responses,” and would notify USDA and state public health officials.

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10. What the 2024 Actions Do Not Do

• No ban on raw milk within states. Sales of raw milk inside a state’s borders remain a matter of state law. The June 2024 letter gave recommendations to states; it did not change any state’s rules.
• No finding that people caught H5N1 from milk. The FDA said in June 2024 that it did not know whether the virus can pass to people through raw milk or raw-milk products. Its later update (March 2025) said it was not aware of any H5N1 illnesses from eating aged raw-milk cheese.
• No new rule. The steps were surveys, studies, letters and a sampling assignment, carried out under existing law and the existing Grade “A” milk program; nothing was published as a rule in the Federal Register.
• No measure of herd infection. The FDA states that its retail survey was not designed to measure how common H5N1 is in dairy herds, and a product’s place of purchase or processing does not show where its milk was produced.
• No animal-health orders. Testing of herds and orders on moving cattle are USDA actions, outside the scope of this page.

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11. Dates and Status as of 11 October 2026

Because the 2024 response consisted of testing and letters rather than a rule, there is no proposed or final rule whose status could change. No later FDA document found for this page withdraws the 2024 statements or recommendations. Later FDA documents add the following:

• 17 January 2025: the FDA’s Center for Veterinary Medicine determined that makers of cat and dog food covered by its preventive-controls rule for animal food, and using uncooked or unpasteurized materials from poultry or cattle (such as uncooked meat, unpasteurized milk or unpasteurized eggs), must reanalyze their food safety plans to include H5N1 as a “known or reasonably foreseeable hazard.” The update cites cases of H5N1 in domestic and wild cats in California, Colorado, Oregon and Washington associated with eating contaminated food products. The FDA reissued it on 30 September 2025 as a seasonal reminder.
• 14 March 2025: the FDA reported that it had sampled 464 pasteurized dairy products in total (milk, cheese, butter and ice cream), all negative for live H5N1. For the cheese assignment, 110 of a planned 299 samples had been collected by 10 March 2025; 96 were PCR-negative and 14 were still being tested, with final results expected later that spring.
• Aged-cheese research: the same update described FDA- and New York State-funded university research, previewed in a pre-print, suggesting that aging raw-milk cheese for 60 days or longer “is not effective at eliminating viable H5N1”; the virus survived through and beyond 60 days of aging in non-heat-treated raw-milk cheese. Heating raw milk at 54°C (130°F) for at least 15 minutes or 60°C (140°F) for at least 10 seconds inactivated the virus in that research, and cheese made at pH 5.0 saw rapid inactivation while pH 6.6 or 5.8 did not. The FDA said more research is needed to know whether pH adjustment is practical, and recommended that processors not use milk from infected cows to make raw-milk products.

Status as of 11 October 2026: complete as a 2024 response; no rule involved. The FDA’s investigation page was last updated on 14 March 2025, and it did not yet report final results of the aged-cheese assignment or the silo study. A query of the Federal Register for FDA documents mentioning H5N1, avian influenza or raw milk from January 2024 through 11 October 2026 found no rule, order or notice about milk safety and H5N1. No later page on this site covers the story.

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12. How the Response Fits the Federal-State Milk Safety System

The FDA framed every step as a check on an existing system rather than a new one. Its documents describe that system this way:

• The Grade “A” program: nearly all (99%) of the commercial milk produced on U.S. dairy farms comes from farms that take part in the federal-state Grade “A” Milk Safety Program and follow the Pasteurized Milk Ordinance (PMO), which the FDA says “includes controls that help ensure the safety of dairy products.”
• Pasteurization: required time and temperature conditions are set in federal regulation (21 CFR 1240.61) and the PMO. The FDA describes pasteurization as having protected public health “for more than 100 years.”
• Abnormal milk: the FDA expects PMO requirements to keep clinically ill cows producing abnormal milk out of the milking herd, which it describes as one of two key measures alongside pasteurization.
• The National Conference on Interstate Milk Shipments: named in the FDA–USDA letters as a coordinator of the silo study, alongside the two agencies, and as one of the three parties that were to review its results.

Seen this way, the 2024 work asked a narrow question — whether this system, built for bacteria and other known pathogens, also handles a virus newly found in cows’ milk — and the FDA’s answer for pasteurized products was that it does. The open questions it identified concerned raw milk and raw-milk cheese, which skip pasteurization. Other 2024 food-safety actions are on the site’s pages on lead in ground cinnamon and mushroom edibles; influenza in people is covered on the Influenza page.

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13. Primary Documents

1. U.S. Food and Drug Administration. Investigation of Avian Influenza A (H5N1) Virus in Dairy Cattle. Program page with dated updates, 25 April 2024 – 14 March 2025 (content current as of 14 March 2025). Not a Federal Register document; no docket — fda.gov program page
2. U.S. Food and Drug Administration (2024). Letter to State, Territorial, Local and Tribal Health Partners on HPAI H5N1 and raw milk, 6 June 2024 — fda.gov letter (PDF)
3. U.S. Food and Drug Administration (2024). FDA Research Agenda for 2024 Highly Pathogenic H5N1 Avian Influenza, as of 24 June 2024 — fda.gov research agenda (PDF)
4. U.S. Food and Drug Administration and U.S. Department of Agriculture (2024). Letter to the Dairy Processing Industry, 30 September 2024 — fda.gov letter (PDF)
5. U.S. Food and Drug Administration and U.S. Department of Agriculture (2024). Letter to Dairy Retailers, 30 September 2024 — fda.gov letter (PDF)
6. U.S. Food and Drug Administration. Microbiological Surveillance Sampling: FY25 Aged Raw Cow’s Milk Cheese Collection and Analysis for HPAI. Assignment page, issued 23 December 2024 (content current as of 30 December 2024) — fda.gov sampling assignment
7. U.S. Food and Drug Administration, Center for Veterinary Medicine (2025). Cat and Dog Food Manufacturers Required to Consider H5N1 in Food Safety Plans. CVM Update, 17 January 2025, reissued 30 September 2025 — fda.gov CVM update

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Key Research Papers

1. Spackman E, Anderson N, Walker S, Suarez DL, Jones DR, McCoig A, Colonius T, Roddy T, Chaplinski NJ (2024). Inactivation of Highly Pathogenic Avian Influenza Virus with High-temperature Short Time Continuous Flow Pasteurization and Virus Detection in Bulk Milk Tanks. Journal of Food Protection 87(10):100349 — PubMed PMID: 39154916
2. Spackman E, Jones DR, McCoig AM, Colonius TJ, Goraichuk IV, Suarez DL (2024). Characterization of highly pathogenic avian influenza virus in retail dairy products in the US. Journal of Virology 98(7):e0088124 — PubMed PMID: 38958444
3. Suarez DL, Goraichuk IV, Killmaster L, Spackman E, Clausen NJ, Colonius TJ, Leonard CL, Metz ML (2025). Testing of Retail Cheese, Butter, Ice Cream, and Other Dairy Products for Highly Pathogenic Avian Influenza in the US. Journal of Food Protection 88(1):100431 — PubMed PMID: 39662738
4. Burrough ER, Magstadt DR, Petersen B, Timmermans SJ, Gauger PC, Zhang J, Siepker C, Mainenti M, Li G, Thompson AC, Gorden PJ, Plummer PJ, Main R (2024). Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024. Emerging Infectious Diseases 30(7):1335-1343 — PubMed PMID: 38683888
5. Caserta LC, Frye EA, Butt SL, Laverack M, Nooruzzaman M, Covaleda LM, Thompson AC, Koscielny MP, Cronk B, Johnson A, Kleinhenz K, Edwards EE, Gomez G, Hitchener G, Martins M, Kapczynski DR, Suarez DL, Alexander Morris ER, Hensley T, Beeby JS, Lejeune M, Swinford AK, Elvinger F, Dimitrov KM, Diel DG (2024). Spillover of highly pathogenic avian influenza H5N1 virus to dairy cattle. Nature 634(8034):669-676 — PubMed PMID: 39053575
6. Guan L, Eisfeld AJ, Pattinson D, Gu C, Biswas A, Maemura T, Trifkovic S, Babujee L, Presler R Jr, Dahn R, Halfmann PJ, Barnhardt T, Neumann G, Thompson A, Swinford AK, Dimitrov KM, Poulsen K, Kawaoka Y (2024). Cow’s Milk Containing Avian Influenza A(H5N1) Virus — Heat Inactivation and Infectivity in Mice. New England Journal of Medicine 391(1):87-90 — PubMed PMID: 38785313
7. Kaiser F, Morris DH, Wickenhagen A, Mukesh R, Gallogly S, Yinda KC, de Wit E, Lloyd-Smith JO, Munster VJ (2024). Inactivation of Avian Influenza A(H5N1) Virus in Raw Milk at 63°C and 72°C. New England Journal of Medicine 391(1):90-92 — PubMed PMID: 38875103
8. Uyeki TM, Milton S, Abdul Hamid C, Reinoso Webb C, Presley SM, Shetty V, Rollo SN, Martinez DL, Rai S, Gonzales ER, Kniss KL, Jang Y, Frederick JC, De La Cruz JA, Liddell J, Di H, Kirby MK, Barnes JR, Davis CT (2024). Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in a Dairy Farm Worker. New England Journal of Medicine 390(21):2028-2029 — PubMed PMID: 38700506

Papers 1–3 are by USDA Agricultural Research Service and FDA scientists and report the studies the FDA announced: paper 1 is the continuous-flow pasteurization study named on the FDA page; paper 2 describes the 297 retail samples collected 18–22 April 2024 from 17 states, representing 132 processors in 38 states, with viral RNA in 60 (20.2%); paper 3 reports retail testing of cheese, butter, ice cream and other dairy products. Paper 4 describes infection in dairy cattle and fatal infection in domestic cats fed raw colostrum and milk from affected cows in Kansas and Texas. Paper 5 reports the spillover of the virus into dairy cattle. Papers 6 and 7 are laboratory studies of heating milk that contained the virus, and paper 8 reports a human infection in a dairy farm worker.

PubMed Topic Searches

1. PubMed: H5N1 in dairy cattle and milk
2. PubMed: avian influenza inactivation by milk pasteurization
3. PubMed: H5N1 and raw-milk cheese
4. PubMed: H5N1 in cats and raw milk

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Connections

• FDA Actions of 2024
• FDA and Regulation
• Raw vs Pasteurized Milk
• Milk
• Influenza
• FDA Lead Alerts on Ground Cinnamon (2024)
• Amanita Muscaria and Mushroom Edibles (2024)
• Brominated Vegetable Oil Revocation (2024)
• PFAS Grease-Proofing Leaves Food Packaging (2024)
• Yogurt and Type 2 Diabetes Claim (2024)
• Infant Botulism Outbreak Linked to Powdered Formula (2025)

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