Since it first appeared in dairy cows in the American South in early 2024, H5N1 bird flu has hopscotched across the nation. While the virus has existed in some form for decades, this particular outbreak has seen the infection of mammals at an unprecedented rate, raising the danger to humans.
Since our last article on H5N1, the virus has spread to over a hundred new farms. However, there is reason for optimism. While some parts of the country are still seeing outbreaks, it isn’t spreading as uncontrollably as it did earlier this year. One notable success story comes from Michigan, which was once the outbreak’s epicenter. Despite being known for testing for the virus more, the state is no longer consistently reporting infections in new farms. One potential factor is that farmers there have been more cooperative with officials than in other states. This has allowed for more aggressive testing for the virus. A positive side effect of this is that scientists can study the outbreak in detail. As a result, Michigan has been the leading source of studies on H5N1 in cows.
The current strain of H5N1 has rapidly moved between species. Source
Nationally, things seem to be moving in a similar direction, though more slowly. Wastewater tracking shows that H5N1 levels have steadily declined for months. The virus is undoubtedly still circulating, but nowhere near levels seen in May, when monitoring for H5N1 began. At the same time, the reported number of newly affected farms has also begun leveling off. This is despite an increase in testing in Colorado, which instituted a mandatory bulk tank testing order to monitor for the virus more aggressively. Of course, considering how flawed H5N1 surveillance is in the US, all data must be rigorously analyzed, but this combination of improving trends suggests a real slowdown in H5N1 spread.
Data from 192 wastewater surveillance sites shows a significant reduction in H5N1 circulation. Source
Despite the outbreak’s deceleration, the past few months have seen several concerning stories emerge. Oklahoma, for example, announced its first outbreak in July—three months after it occurred. In New Mexico, cows on a raw milk farm came down with H5N1-like symptoms, potentially exposing customers. Mark McAfee, owner of a raw milk operation in California, alerted the FDA of the outbreak. Even so, no investigations took place and New Mexico wasn’t even informed until the LA Times reached out.
In Colorado, the virus has been particularly rampant. In part due to the dense concentration of farms in the state, H5N1 spread to more than 60 of the state’s 106 dairy farms. Infections were so rampant that it even spread to poultry on three egg-laying farms. This forced the state to send workers to cull millions of birds, putting people in dangerously close contact with the virus. So far, the state has reported ten human infections.
Challenges Ahead
Although it’s impossible to know for sure, the nation’s biggest dairy producers—California, Wisconsin, and New York—haven’t yet had H5N1 outbreaks. California alone is home to 1.69 million cows compared to Colorado’s 200,000. A similar outbreak there could result in far more economic impact and human infections. Considering how rapidly cases exploded in large producers like Texas without control measures, these large states will have to remain vigilant until H5N1 is virtually eradicated.
Major milk-producing states in the US. Source
Meanwhile, hundreds of county fairs are expected to take place this fall, bringing thousands of people and farm animals together in dozens of states. It doesn’t help that these are concentrated in farm states hit hard by H5N1. Usually taking place from July to October, fairs have been associated with swine flu outbreaks in people in the past. With H5N1 widespread in American farm animals for the first time, the risks cannot be understated.
Perhaps even more concerningly, flu season is approaching, posing three major risks. First, flu tends to spread better in colder weather, Additionally, as all types of respiratory diseases spread, H5N1 cases could be misdiagnosed. Currently, the CDC monitors flu-related emergency room visits for signs of H5N1 outbreaks, but as flu cases surge in the winter, that could become complicated. Finally, as seasonal flu cases increase, it becomes far more likely for people to catch both H5N1 and seasonal flu, allowing the viruses to share genes in a process called “reassortment.” This is likely how the last three flu pandemics started.
Reassortment plays a crucial role in the emergence of new flu pandemics. Source
To help counter this threat, the CDC is launching a $5 million initiative to vaccinate farm workers. $2 million will go towards procuring flu shots for at-risk personnel (which may include hundreds of thousands of people nationwide), and $3 million will fund outreach efforts.
The next few months will be crucial in determining whether the nation can control H5N1 or if it will spiral into a more serious crisis. The current slowdown in infections provides some hope, but stronger containment measures are still vital, whether in states still struggling with outbreaks or states that have yet to be hit.
The CDC’s vaccination initiative is a step in the right direction, aiming to protect those most at risk. However, it will take more than vaccines to stave off a potential crisis. Public awareness, swift reporting of new cases, and continued research into H5N1's behavior in cows and other mammals will be essential to understanding and curbing this outbreak.
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