H5N1 Avian Flu Crisis: The Growing Threat to US Food Supply and Public Health

Bird flu. Black raven perched on a blue virus sphere against a turquoise background.

(Adobe Stock 1164288282 by Happy Photo Stock)

The US could be on the precipice of enduring another pandemic. It is not one from Southeast Asia, but one largely grown and in some respects nurtured in North America, as evidenced by the rising number of avian influenza (flu) (H5N1) cases and the muted response of our public health system. As of January 2025, there have been 67 reported human cases of H5N1 in the US and 1 death.¹ However, confirmed cases of human-to-human spread have not yet been reported. Since January 2022, there have been 1490 bird outbreaks affecting over 150 million animals.² Over the last year, there have also been 957 confirmed cases in cattle, with 736 cases in California.³

Although largely ignored until recently, the H5N1 virus has existed for over a century. This virus was first observed in the 1880s,⁴ and the first outbreak in the US occurred in 1924.

The H5N1 clade that infects birds is B3.6.⁵ However, the virus is constantly mutating and optimizing its ability to infect various mammalian species. H5N1 has infected harbor and grey seals, American minks, South American sea lions, and cats.⁶ By 2023, 48 mammalian species in 26 countries have contracted the virus.⁷

In March 2024, a clade of the virus (B3.13)⁸ was first detected in dairy cows on farms in Texas, Kansas, and New Mexico.⁹ A single mutation increased the virus’s ability to transmit in cattle.¹⁰ Approximately 10% of the herds were infected, and early in the epidemic, there was little or no associated mortality.⁹ During this time, the American Veterinary Medical Association reported the United States Department of Agriculture (USDA), FDA, and CDC “indicated they [had] no concerns about the safety of the commercial milk supply.”⁹

By October 2024, a new, more lethal clade appeared in California dairy herds, with cows dying at a much higher rate.¹¹ Mortality rates were 15% to 20% compared with 2% in other states. In November, the National Academy of Sciences reported that 15% of the infected herds became critically ill with decreased feed intake and milk production.¹² The primary route of infection is thought to be mammary inoculation through the process of milking. The cow’s milk can become contaminated, and drinking raw milk poses significant public health risks.¹³

Seven percent of dairy workers on farms with H5N1 outbreaks have had positive test results for the virus.¹⁴ The symptoms are usually mild, with conjunctivitis being a common symptom. No deaths have been reported.

Although the condition has been mild in humans, farm cats have developed neurological signs and rapid death after drinking raw milk from infected cows.¹⁵ This represents mammal-to-mammal spread. In January 2025, the FDA reported that more than a dozen cats had died from avian flu after eating raw pet food.¹⁶

On December 18, 2024, Governor Newsom of California declared a state of emergency prompted by the H5N1 virus’ infection of dairy herds and its detection in milk products.¹⁷ Mechanization with robotic milking machines is one strategy to minimize the spread of the virus in dairy herds and reduce farm worker exposure.¹⁸ The cows are trained to approach the machines, where robotic arms and cameras do the rest. Between milkings, the machines use an iodine solution to clean themselves.

Despite the ongoing threat to our food supply, the US has not had an aggressive response to stop the spread of H5N1: In April 2024, the USDA enacted testing and reporting requirements for lactating dairy cattle traveling across state lines,¹⁹ but other livestock (heifers, dry cows, and bull calves) did not require testing, and no testing was required within the various states with outbreaks.

• In April 2024, the USDA required reporting for livestock with positive test results for H5N1.
• In December 2024, a national milk testing strategy was implemented to safeguard the public and help eliminate the virus from dairy cattle.²⁰
• On January 16, 2025, the CDC issued an advisory notice recommending that hospitals subtype flu to better detect H5N1.²¹
• On January 21, 2025, public communications from the US health agencies (FDA, CDC, National Institutes of Health) were paused. This included CDC health alerts, website updates, and Morbidity and Mortality Weekly Report (MMWR) publications. The following week, 3 MMWR publications regarding the H5N1 outbreak would have been published.²²
• On January 23, 2025, The Bullvine reported that the USDA is fast-tracking vaccine development for dairy cattle.²³

Although H5N1 vaccines are highly effective and are used by the Netherlands and France in poultry, the USDA has not authorized vaccine use due to its potential adverse impact on poultry exports.²⁴

Currently, avian flu is devastating our food supply and driving up food prices, including eggs and poultry.²⁵ More than 100 million birds have died or been culled to prevent further spread.²⁵ When poultry and eggs are in short supply, the public purchases other food items, increasing prices. Politicians initially blamed corporate price gouging instead of acknowledging an uncontrolled avian flu.²⁶

Human outbreaks and taking definitive steps to minimize viral spread

Thus far, humans have been largely spared. This is largely because H5N1 uses the α-2,3 receptor to infect birds and mammals.²⁷ This receptor is found in almost all animals, including humans. However, in humans, this receptor is primarily located in the lower respiratory tract, with the α-2,6 receptor being the dominant receptor in the upper respiratory tract.²⁸ Thus, in its present form, the H5N1 virus does not readily infect humans; when it does, it rarely spreads to other humans.

Unfortunately, the virus is on the verge of adapting to more readily infect humans through 2 possible mechanisms. The first is recombination (antigenic shift) with a seasonal flu virus that is fully adapted to infect humans. This requires simultaneous infection of the 2 viruses in an animal. The 2 most likely possibilities are a pig with α-2,3 and α-2,6 receptors and a human, such as a dairy worker who goes to work with the seasonal flu and then contracts avian flu. The resultant virus would be entirely new, and its infectivity and pathogenicity would be uncertain.

The second method is by mutation (antigenic drift). A decade ago, several different mutations would have had to occur before there was a risk of significant human-to-human spread, but the virus has progressively adapted. Scripps Research has reported that we are only 1 mutation away from H5N1 efficiently spreading in humans.²⁹

According to the CDC, the fatal human case in Louisiana and the severe case in a teenager in Canada³⁰ have shown similar mutations (in variant D1.1) that could enable the spread between humans.³¹ Both dangerous strains were quickly identified and contained, preventing spread to the general population.

Unfortunately, according to the USDA,³² the D1.1 variant has become the predominate genotype in the North American Flyways. D1.1 has been detected in dairy cattle in Nevada. Spilling over to cattle poses not only a threat to animal farm workers but also to the general public.

Response and Vaccines

A rigorous response to the H5N1 threat is desperately needed. Unfortunately, surveillance for H5N1 is spotty at best and mainly focused on dairy cattle. The lack of a robust surveillance system and data has allowed many in the public and our leadership to ignore this pandemic. At a minimum, expanded testing and enhanced reporting are needed to help secure our food industry.

Vaccines are also paramount in stopping a potential avian flu pandemic. Finland has proactively offered H5N1 vaccinations to animal farm workers. In December 2024, the United Kingdom stockpiled 5 million vaccine doses, enough for 8.2% of its population.³³ The European Union has ordered 40 million doses,³⁴ and in June 2024, the US ordered 4.8 million doses,³⁵ enough for 1.4% of its population.³⁴

Most recently, in January 2025, Moderna was awarded $590 million for an mRNA avian flu vaccine.³⁶ The exact genetic composition of the potential human variant is unknown. If human adaptation does occur, mRNA technology provides the fastest response.

Hopefully, our population might be building up a degree of immunity. The seasonal flu vaccine may provide some protection against H5N1. Findings from one study have observed that 12.2% to 15% of vaccinated individuals developed protective antibodies to avian flu 1 month after vaccination.³⁷ In addition, a degree of immunity might also develop in our population from exposure to inactivated viruses in contaminated food.

Thus, although the potential for a devastating H5N1 pandemic in the US is still uncertain, we need to prepare for the worst while hoping for the best. Actions such as the state of Louisiana prohibiting their health department from promoting vaccines are both dangerous and counterproductive, especially in the state that recently had a fatal case of a dangerously mutated H5N1 virus.³⁸

Few can comprehend or imagine what it was like to live in fear of infectious diseases before vaccines. However, if we do not develop a uniform, effective response to emerging pathogens, we will experience this horrible reality firsthand. We need public health cooperation, not social confrontation. We must follow the science that has demonstrated the effectiveness and safety of N95 masks, vaccines, and clean indoor air so we do not have to live through another pandemic. A pandemic that devastates not only our food supply but also our health and the foundations of our society. 

References

1. H5 bird flu: current situation. CDC. January 24, 2025. Accessed January 24, 2025. https://www.cdc.gov/bird-flu/situation-summary/index.html
2. USDA reported H5N1 bird flu detections in poultry. CDC. January 17, 2025. Accessed January 24, 2025. https://www.cdc.gov/bird-flu/situation-summary/data-map-commercial.html
3. HPAI confirmed cases in livestock. US Department of Agriculture. Updated January 16, 2025. Accessed January 24, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-flu/hpai-detections/hpai-confirmed-cases-livestock
4. 1880-1959 highlights in the history of avian flu (bird flu) timeline. CDC. April 30, 2024. Accessed January 24, 2025. https://www.cdc.gov/bird-flu/avian-timeline/1880-1959.html
5. H5N1 highly pathogenic avian flu (HPAI) in livestock information for small ruminant (sheep and goat) and camelid stakeholders. US Department of Agriculture. Accessed January 24, 2025. https://www.aphis.usda.gov/sites/default/files/small-ruminant-camelid-h5n1-info.pdf
6. Table 1 H5N1 clade 2.3.4.4b outbreaks in mammals. Nature. Accessed January 24, 2025. https://www.nature.com/articles/s41586-024-08054-z/tables/1
7. Plaza PI, Gamarra-Toledo V, Rodríguez Euguí J, Lambertucci SA. Recent changes in patterns of mammal infection with highly pathogenic avian flu A(H5N1) virus worldwide. Emerg Infect Dis. 2024;30(3):444-452. doi:10.3201/eid3003.231098
8. Webby RJ, Uyeki TM. An update on highly pathogenic avian flu A(H5N1) virus, clade 2.3.4.4b. J Infect Dis. 2024;230(3):533-542. doi:10.1093/infdis/jiae379.
9. Highly pathogenic avian flu found in Texas, Kansas dairy cattle. American Veterinary Medical Association. March 26, 2024. Accessed January 24, 2025. https://www.avma.org/news/highly-pathogenic-avian-flu-found-texas-kansas-dairy-cattle
10. Good MR, Fernández-Quintero ML, Ji W, et al. A single mutation in dairy cow-associated H5N1 viruses increases receptor binding breadth. Nat Commun. 2024;15(1):10768. doi:10.1038/s41467-024-54934-3
11. Douglas L. Cows dead from bird flu rot in California as heat bakes dairy farms. Reuters. October 17, 2024. Accessed January 24, 2025. https://www.reuters.com/world/us/cows-dead-bird-flu-rot-california-heat-bakes-dairy-farms-2024-10-17/
12. Potential research priorities to inform readiness and response to highly pathogenic avian flu A (H5N1): a workshop. National Academies. Accessed January 24, 2025. https://www.nationalacademies.org/our-work/potential-research-priorities-to-inform-readiness-and-response-to-highly-pathogenic-avian-flu-a-h5n1-a-workshop
13. The dangers of raw milk: unpasteurized milk can pose a serious health risk. FDA. May 30, 2024. Accessed January 24, 2025. https://www.fda.gov/food/buy-store-serve-safe-food/dangers-raw-milk-unpasteurized-milk-can-pose-serious-health-risk
14. Mellis AM, Coyle J, Marshall KE, et al. Serologic evidence of recent infection with highly pathogenic avian flu A(H5) virus among dairy workers - Michigan and Colorado, June-August 2024. MMWR Morb Mortal Wkly Rep. 2024;73(44):1004-1009. doi:10.15585/mmwr.mm7344a3
15. Burrough ER, Magstadt DR, Petersen B, et al. Highly pathogenic avian flu A(H5N1) clade 2.3.4.4b virus infection in domestic dairy cattle and cats, United States, 2024. Emerg Infect Dis. 2024;30(7):1335-1343. doi:10.3201/eid3007.240508
16. Tin A. More than a dozen cats dead or sickened by bird flu in raw pet food, FDA says. MSN. Accessed January 24, 2025. https://www.msn.com/en-us/news/us/more-than-a-dozen-cats-dead-or-sickened-by-bird-flu-in-raw-pet-food-fda-says/ar-AA1xAMIs
17. Governor Newsom takes proactive action to strengthen robust state response to bird flu. Governor Gavin Newsom. December 18, 2024. Accessed January 24, 2025. https://www.gov.ca.gov/2024/12/18/governor-newsom-takes-proactive-action-to-strengthen-robust-state-response-to-bird-flu/
18. Anthes E. How the messy process of milking cows can spread bird flu. New York Times. December 5, 2024. Accessed January 24, 2025.https://www.nytimes.com/2024/12/05/science/bird-flu-milk-dairy-h5n1.html
19. APHIS Requirements and Recommendations for Highly Pathogenic Avian Flu (HPAI) H5N1 Virus in Livestock for State Animal Health Officials, Accredited Veterinarians and Producers. US Department of Agriculture. May 14, 2024. Accessed January 24, 2025. https://www.aphis.usda.gov/sites/default/files/aphis-requirements-hpai-livestock-eng-sp.pdf
20. National milk testing strategy. US Department of Agriculture. Updated January 10, 2025. Accessed January 24, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-flu/hpai-detections/livestock/nmts
21. Whitacre Martonicz T. CDC issues H5N1 health advisory: infection preventionists urged to strengthen avian flu surveillance and response. Infection Control Today. January 17, 2025. Accessed January 24, 2025. https://www.infectioncontroltoday.com/view/cdc-issues-h5n1-health-advisory-infection-preventionists-urged-strengthen-avian-flu-surveillance-and-response
22. Why cutting off health communications puts us all at risk. LinkedIn. January 24, 2025. Accessed January 24, 2025. https://www.linkedin.com/pulse/why-cutting-off-health-communications-puts-us-mffbc/
23. USDA fast-tracks H5N1 vaccine development for dairy cattle amid outbreak concerns. The Bullvine. January 23, 2025. Accessed January 24, 2025. https://www.thebullvine.com/news/usda-fast-tracks-h5n1-vaccine-development-for-dairy-cattle-amid-outbreak-concerns/
24. Howarth T. Why is the US not vaccinating poultry against bird flu? Newsweek. January 6, 2025. Accessed January 24, 2025. https://www.newsweek.com/why-us-not-vaccinating-poultry-against-bird-flu-2010511
25. Yurkevich V. Egg prices are going even higher: this time it’s avian flu and the holidays. CNN. November 24, 2024. Accessed January 24, 2025. https://www.cnn.com/2024/11/24/business/avian-flu-holidays-egg-prices/index.html
26. Cohen B. The issues: Harris’ anti-price gouging proposal. FactCheck.org. October 28, 2024. Accessed January 24, 2025. https://www.factcheck.org/2024/10/the-issues-vice-president-harris-anti-price-gouging-proposal/
27. Fig. 5: how IAVs adapt to new host species. Nature. Accessed January 24, 2025. https://www.nature.com/articles/s41586-024-08054-z/figures/5
28. Vaccine development: focus on bird flu, H5N1. YouTube. https://www.youtube.com/watch?v=ZB-g-pZif6U
29. Scripps Research scientists identify mutation that could facilitate H5N1 “bird flu” virus infection and potential transmission in humans. News release. Scripps Research. December 5, 2024. Accessed January 24, 2025. https://www.scripps.edu/news-and-events/press-room/2024/20241205-wilson-paulson-h5n1.html
30. Whitacre Martonicz T. Avian flu: latest developments and should we be concerned? Infection Control Today. Accessed January 24, 2025. https://www.infectioncontroltoday.com/view/avian-flu-latest-developments-should-we-be-concerned-
31. Tirrell M. We ‘have our head in the sand’: Health experts warn US isn’t reacting fast enough to threat of bird flu. CNN. December 27, 2024. Accessed January 24, 2025. https://www.cnn.com/2024/12/27/health/cdc-bird-flu-virus-mutations-analysis/index.html
32. Animal and Plant Health Inspection Service. APHIS confirms D1.1 genotype in dairy cattle in Nevada. USDA. Published January 31, 2025. Accessed February 13, 2025. https://www.aphis.usda.gov/news/program-update/aphis-confirms-d11-genotype-dairy-cattle-nevada-0
33. Shaw I. UK stockpiles 5 million bird flu vaccines amid fears highly pathogenic H5N1 virus will spark the next pandemic. Sun. December 3, 2024. Accessed January 24, 2025. https://www.thesun.co.uk/health/32075603/uk-stockpile-bird-flu-vaccines-pathogenic-pandemic-h5n1/
34. Payne J. EU to secure 40 million avian flu vaccines for 15 countries - officials. Reuters. June 10, 2024. Accessed January 24, 2025. https://www.reuters.com/business/healthcare-pharmaceuticals/eu-secure-40-million-avian-flu-vaccines-15-countries-officials-2024-06-10/
35. Lucey DR. U.S. orders 4.8 million doses of a cell-based, adjuvanted H5-vaccine for avian flu preparedness. Infectious Diseases Society of America. June 5, 2024. Accessed January 24, 2025. https://www.idsociety.org/science-speaks-blog/2024/u.s.-orders-4.8-million-doses-of-a-cell-based-adjuvanted-h5-vaccine-for-avian-flu-preparedness
36. Benadjaoud Y, Deliso M. Moderna awarded $590M to help accelerate development of mRNA-based bird flu vaccine: HHS. ABC News. January 17, 2025. Accessed January 24, 2025. https://abcnews.go.com/Health/moderna-mrna-bird-flu-vaccine-award/story?id=117813010
37. Sanz-Muñoz I, Sánchez-Martínez J, Rodríguez-Crespo C, et al. Are we serologically prepared against an avian flu pandemic and could seasonal flu vaccines help us? mBio. 2024;e0372124. doi:10.1128/mbio.03721-24
38. Westwood R. Louisiana forbids public health workers from promoting COVID, flu and mpox shots. NPR. December 20, 2024. Accessed January 24, 2025. https://www.npr.org/sections/shots-health-news/2024/12/20/nx-s1-5223440/louisiana-ban-public-health-promoting-covid-flu-mpox-vaccines-landry-rfk-jr-anti-vaccine