H5N1, The Pandemic That Isn't?

An Unseen Pandemic in the Making

As world leaders attempt to move COVID-19 into the rearview mirror, another potential health crisis is brewing in the background—one that most people haven’t heard about but could prove to be even more devastating.

H5N1, commonly known as avian influenza, resurfaced and rapidly mutated in late 2023. It quietly spread from birds to dairy cows, other mammals, and eventually to humans in small numbers.

Since then, H5N1 has taken a particularly insidious turn, with potential long-term consequences for global public health, agriculture, and food security. And yet, despite the gravity of the situation, media coverage has been limited, and the public remains largely unaware or unconcerned.

While H5N1 has been transmitted to some mammals as far back as 2003, infections since December 2023 have been more rapid and widespread. There have also been a larger range of hosts, demonstrating more adaptability than the virus previously has shown. This has raised further concerns about the possibility for the virus to advance toward human-to-human transmission.

While COVID-19 continues to make global headlines, the spread of H5N1 has unfolded more quietly, despite its consequences potentially being more severe. The minimal media coverage and limited industry transparency makes it harder to understand the scope of the problem, leaving the public dangerously uninformed.

How H5N1 Adapted to Mammals

The origins of H5N1 date back to the 1990s, with periodic outbreaks that mostly affected birds. However, in the last two years, the virus has spread far beyond its traditional hosts, infecting not only poultry but a wider range of mammals such as seals, cats, cattle, and mice.

This marks a significant shift in the behavior of the virus, which is adapting and spreading faster than scientists anticipated. Warning signs first emerged on dairy farms in December 2023, as cats displayed neurological symptoms of H5N1 that proved fatal.

By May 2024, wastewater monitoring picked up traces of H5N1 in multiple U.S. cities, including in Texas, where multiple dairy farms were affected. This indicated the virus may have entered the human population—possibly asymptomatically.

These results coincided with an uptick in Influenza A found in wastewater samples, something incredibly rare for that time of year. However, it wasn’t initially clear if the spike in flu was connected to H5N1. The fact that avian flu was detected in wastewater, however, suggested that human transmission was at least a possibility.

Wastewater Monitoring

During the COVID-19 pandemic, wastewater testing became an early indicator of viral outbreaks in communities. The same methods, applied to H5N1, provided a critical window into the virus’s spread.

By June 2024, the CDC expanded its wastewater monitoring systems, incorporating more advanced sub-typing protocols to differentiate between seasonal flu (influenza A) and H5N1 .

Despite these efforts, early testing in May revealed significant uncertainty about whether the virus was being transmitted between humans or simply shedding from infected animals.

A key challenge in wastewater monitoring is distinguishing the source of viral particles. Wastewater can contain traces of flu from humans, animals, and even animal products like milk.

This complicates efforts to determine the true extent of human exposure. Early detections of H5N1 in May signaled the possibility that the virus was spreading through various means, but it was clear it had moved beyond its avian hosts.

While H5N1’s primary carriers have always been birds, the virus’s ability to cross into mammals and even humans raises alarm bells. By June, scientists confirmed house mice in New Mexico had tested positive for H5N1, bringing the virus yet closer to human environments—offices, homes, and even food production facilities.

This marked a turning point, as the virus could now spread via multiple vectors, including contaminated surfaces and animal waste. The ability for the virus to survive and spread through new species created a complex web of transmission that only becomes more difficult to manage as time passes.

A Cover-up? The Dairy Industry v. Pandemic Response

Experts originally said it was highly unlikely H5N1 would be able to spread from human-to-human. However, with the rapid development of the virus in 2024, that reality is more of a possibility, prompting the CDC to ask states to provide PPE to farmworkers and slaughterhouse employees.

However, the CDC also said it wouldn’t push for access to farms, underscoring the complex jurisdictional boundaries that allow farms to limit government oversight and testing of their animals.

In April 2024, the veterinarians who originally treated dairy cows sick with H5N1 attempted to rename the virus to “Bovine Bird Flu” to prevent panic. And the Agriculture Secretary of Pennsylvania stated, “Decouple it from an FDA and a CDC issue. This is a workforce issue that ought to be expressed from the USDA and Secretary Tom Vilsack.”

On the surface, this may look like a decision about jurisdiction and preserving the livelihoods of small farms. However, the context surrounding Tom Vilsack’s role in the USDA raises questions. A Biden appointee, Vilsack previously served as the President of the U.S. Dairy Export Council, and his background includes lobbying for the dairy industry.

Nevertheless, the rise of Influenza A in wastewater in May was troubling, especially given it is a typically low-flu season. This surge, which coincided with the rise of H5N1 on dairy farms, was unusual and concerning.

The Dairy Dilemma

One of the most concerning aspects of the 2023-24 H5N1 outbreak is its rapid spread among dairy herds. While previous H5N1 outbreaks were largely confined to wild birds and poultry. This time, however, the virus made a successful transition into the dairy industry, which plays a significant role in the U.S. food system.

By September 2024, the USDA had reported that 238 dairy herds in the U.S. had confirmed cases of the virus. Some cows exhibited reduced appetite, milk abnormalities, and lower milk production.

The spread of H5N1 to cattle is a significant development, as it not only impacts agricultural productivity but also poses a new risk for zoonotic transmission. In this case, the virus has come closer to more effectively jumping from animals to humans, which could more quickly develop into human-to-human transmission.

The economic impact of this spread was immediate. The dairy industry, already under strain due to labor shortages and other challenges, faced severe disruptions. States like Iowa and Michigan, where the outbreaks were most widespread, declared disaster situations as early as June, culling millions of infected birds and cattle.

As the virus spread through dairy herds, farmworkers were put at significant risk. Despite the dangers, protective measures were often inadequate, and many workers—particularly undocumented workers—are reluctant to report symptoms or seek testing due to fears of losing their jobs.

By June 2024, there were isolated reports of human infections among farmworkers in Michigan and Texas, raising concerns about the potential for wider outbreaks. However, testing remained limited, and the majority of workers were not screened for H5N1 unless they displayed clear symptoms.

What the Wastewater Says Now

Perhaps one of the most alarming aspects of the H5N1 outbreak is how it is tracked—or, more precisely, how difficult it is to track. Wastewater monitoring, which gained prominence in the COVID-19 pandemic, was an invaluable tool for identifying viral spread before clinical symptoms appear. But in the case of H5N1, it has its limits.

Throughout May and June 2024, wastewater data showed high levels of influenza A, but it was initially impossible to differentiate between seasonal flu and H5N1. While the CDC later implemented new sub-typing protocols that distinguishes between these viruses, the early stages of the outbreak were clouded with confusion.

Even with advanced sub-typing, distinguishing between viral inputs from humans and animals remains a challenge. This is especially the case in regions with high agricultural activity, where animal waste contributes to wastewater samples.

By October 2024, the CDC confirmed that H5N1 was still detected in wastewater, with the highest levels reported near large dairy and poultry farms. These findings are concerning, not only because they show the virus is still circulating, but also because wastewater detection is often a precursor to a larger outbreak. Now that we’re well into flu season, public health officials are bracing for the possibility that H5N1 could become more widespread.

Pigs: The Final Barrier

Although human cases of H5N1 are rare so far, the virus’s ability to infect mammals, including livestock, suggests it may be only a matter of time before larger outbreaks occur among humans.

In April 2024, the first cases of H5N1 in farmworkers were reported, with both symptomatic and asymptomatic individuals identified in Michigan and Texas. These workers had direct contact with infected animals, primarily dairy cows, and experienced mild symptoms like conjunctivitis. While these cases did not lead to significant illness or death, they raised concerns about how easily the virus could spread in settings with poor protective measures.

Despite the fact that PPE is now widely used in these settings, there are indications that H5N1 is likely underreported. One such indication is the marked drop in milk production throughout California.

Nathaniel Donnay, Director of Dairy Market Insight at StoneX, remarked on California's milk production. Data from 14 states affected by bird flu, including California, he said, show a clear pattern: a significant drop in production lasting several weeks.

Donnay emphasized that both his data and conversations with farmers indicate widespread under-reporting of the disease in dairy herds across the U.S. The higher spread in California, he pointed out, while partly due to the aggressiveness of H5N1, is also because of the state's rigorous testing measures, including testing every herd within six miles of an infected one or herds with an epidemiological link.

An epidemiological link is a connection between animals or environments that may lead to the transmission. It could be shared space or an interaction explains how the disease could spread from one animal to another. For example, if two herds share equipment or are near each other, that is considered an epidemiological link.

A variety of other factors could contribute to this under-reporting. There are massive economic implications for shutting down farms. And, as I’ve already mentioned, the workers—many of whom are undocumented—are reluctant to report symptoms. A combination of low testing rates among workers and the reliance on symptomatic testing has also made it difficult to determine the true scope of the outbreak.

Farmworkers, many of whom work in close proximity to infected livestock, are at the greatest risk. The virus may be spreading through workers asymptomatically, but without widespread testing, public health officials are in the dark. This leaves many wondering if the current outbreak is significantly larger than reported.

Influenza A viruses have a lot of subtypes and can infect many different species, including humans. Wild water birds are the natural home for these viruses, which have caused four pandemics since 1900.

Each of these pandemics came about when an animal virus mutated enough to be able infect humans. Sometimes, this came directly from birds—such as during the 1918 pandemic, the deadliest in modern history until COVID-19.

In other cases, an influenza virus made it to humans through an intermediate mammal species. That’s how it happened in the 2009 pandemic, when the flu was transmitted to humans through pigs.

Pigs are uniquely susceptible to both avian and human influenza viruses, making them a critical mixing vessel. Here, the genetic material of the virus can break apart and change to form new versions of the flu.

This “genetic reassortment” can lead to the emergence of new strains that are more efficiently transmitted to humans, creating the perfect storm for a human-to-human transmission pandemic.

In July 2024, Dr. Catharine Paules, an infectious diseases physician at Penn State, emphasized the importance of monitoring H5N1’s potential spread to pigs. Paules noted that pigs' susceptibility to both avian and human influenza viruses makes them a sort of final barrier.

The concern at that time was that, if H5N1 established itself in pigs, the risk of genetic reassortment and the development of a highly transmissible strain would dramatically increase, potentially leading to a new pandemic.

Then, on October 30, 2024, the first case of H5N1 in pigs was reported on a backyard farm in Oregon. The USDA stated there is no concern about the safety of the nation's pork supply, and the risk to the public remains low.

These developments underscore the virus's adaptability and the challenges in containing its spread, raising concerns about potential public health implications. Despite concerted efforts by agencies such as the USDA, FDA, and CDC, H5N1 has made significant inroads in 2024, expanding beyond birds, infecting dairy cattle, and now pigs.

What Happens Now?

As we head deeper into flu season, there are many unanswered questions about the future trajectory of H5N1. Will the virus make a sustained leap into the human population, or will it remain largely confined to animals?

The government has prepared for the worst, initiating the production of 150 million H5N1 vaccine doses, which would only inoculate 2% of the global population. This underscores the limitations of current preparedness measures. Even if a larger outbreak occurs, vaccine supplies will be critically short.

While it has received less attention compared to COVID-19, media outlets have reported on the spread of H5N1 to mammals and the associated risks. Still, the public remains largely unaware of the pandemic potential of H5N1.

In contrast to COVID-19, which dominated global attention for years, the potential deadly nature of H5N1—with a mortality rate of up to 60 percent—appears to be downplayed to prevent widescale panic. Or perhaps to prevent economic disruption. But as history has demonstrated, viruses don’t wait for the world to catch up.

The Pandemic That Isn’t… Yet

The situation with H5N1 remains fluid, and it is difficult to predict what the next few months will hold. What’s clear, however, is that the virus has already made significant headway with few barriers to entry to achieving human-to-human transmission.

H5N1 isn’t going away. Its ability to adapt, infect mammals, and possibly spread more broadly in humans is a serious concern. Public health authorities need to step up their efforts to monitor, report, and contain H5N1 before it becomes another global health crisis.

For now, it’s the pandemic that isn’t—but it probably will be and sooner than we think.