With the ongoing spread of bird flu in animals and sporadic transmission to humans, tracking the virus has been made even more challenging since we are in the middle of our annual influenza season.
Joseph Bresee, M.D.
Director, Partnership for International Vaccine Initiatives, The Task Force for Global Health
Could bird flu become the next pandemic? It is a growing concern for researchers and epidemiologists like myself and my team at the Partnership for International Vaccine Initiatives (PIVI). Since early last year, the U.S. Centers for Disease Control and Prevention (CDC) has reported 70 cases in the United States of individuals infected by the H5N1 virus, more commonly known as “avian flu” or “bird flu,” as of March 2025. With the ongoing spread of the virus in animals and sporadic transmission to humans, including the first human death reported recently, tracking the virus has been made even more challenging since we are in the middle of our annual influenza season — making it as difficult to find as a needle in a flu-stack.
This year, just like years past, we expect to see hundreds of thousands of hospitalizations — and sadly, several thousand deaths — from seasonal influenza. So, what makes less than 100 human cases of H5N1 influenza in people so worrying? First, we have seen the virus spread rapidly in birds. A typical bird flu virus causes illness and outbreaks in wild and domestic birds. However, since last year, H5N1 has led to widespread outbreaks in domestic poultry flocks and wild birds, and it has been found in all 50 states. Second, unlike other H5 viruses — which have existed around the world for nearly two decades — this virus infects mammals easily, giving pause to scientists who are concerned it could spread more easily to humans. H5N1 has caused infections in dairy cattle in 16 states and is likely to rise. Finally, as of February, 67 cases of H5N1 infections in humans have been reported in 10 states, with one fatality. Almost all human cases have been found in people who have had close exposure to animals infected with the virus, but a few cases have no such animal links, raising concerns about how close we might be to human-to-human spread.
The other factor that makes it difficult to track this virus is its similarity to seasonal influenza and the timing of the rise of this virus in the United States and Canada. Right now, if an individual comes to their doctor complaining of symptoms that typically sound like the flu, providers will test for influenza. If a bird flu pandemic started during flu season, we could have dozens of bird flu cases hiding in plain sight among millions of influenza cases during the early days of the pandemic, and this overlap in illness symptoms would make it difficult to monitor.
Preventing a pandemic
There is good news amid these concerns. For the common seasonal influenza viruses, getting vaccinated each year is still the most effective, safe, and easy way to prevent illness. This is especially important for people at increased risk for influenza, including young children, older adults, pregnant women, and those with chronic health conditions. For these individuals, getting vaccinated must be an integral part of their annual health plan.
The CDC’s current assessment of the H5N1 virus finds the risk to the public remains low. Through its field investigations, national surveillance systems, and careful laboratory work, the CDC is monitoring the situation closely and providing regular updates online. However, it is still important to remain vigilant. Because most human infections come from exposure to infected animals, federal and state authorities have developed programs to reduce the spread of the virus in the United States and to protect people most at risk, including individuals who might be exposed through their jobs or recreational activities. For most of us, the best advice is to avoid direct contact with wild birds and other animals infected or that might be infected with avian influenza viruses, and to avoid touching or consuming food made with raw milk or raw milk products. Infected cows’ milk can contain the virus. Pasteurization will kill avian influenza viruses.
More good news: Over the past twenty years, the United States government has wisely invested in public health research, preparation, and virus surveillance work, preparing our country and countries around the world for the next global influenza pandemic. 13 years ago, PIVI was invited to join this work, charged with helping low-income countries develop rapid response capabilities for influenza vaccinations. This investment yields meaningful results. Across the board, the countries PIVI has been working with for more than a decade to strengthen their vaccination programs were able to respond more quickly and efficiently to the COVID-19 pandemic than countries that did not have influenza vaccination programs in place. As a result of our team’s work, coupled with the life-changing work of the federal government and public health researchers worldwide, we are much better prepared than we have ever been to tackle viruses like bird flu.
Rapid and robust action
This preparedness is paying off now. Some of the vaccines developed for earlier H5 viruses can work for the H5N1 virus, and the United States has doses of these vaccines stockpiled for rapid use if needed. New vaccines specifically developed to protect against this virus are being developed, tested, and produced. Plans for how and when they will be used are well underway. Medications developed for seasonal influenza have also been tested and will be effective against these new viruses. Lessons learned from past outbreak investigations of H5 viruses and from the COVID pandemic response have helped our understanding of how best to prevent transmission to humans. Finally, the surveillance systems that the CDC uses for influenza and other respiratory viruses have been employed for H5N1 monitoring, and together with field investigations, these surveillance systems have enabled authorities to keep close tabs on the virus in case it begins to change, spreads more easily from person to person, or causes more severe illnesses in humans — all signals which might mean the onset of a bird flu pandemic.
It is important to emphasize that the systems we use to monitor, prevent, and treat seasonal influenza each year are also the foundation for being able to respond to epidemics like bird flu quickly and effectively. This is also true for the critical work that organizations like PIVI are doing in developing countries, helping them establish vaccination programs to prevent influenza each year and deploy life-saving vaccines during pandemics. While this work helps lower-income countries, it also reduces the threat our country faces by ensuring that new diseases that emerge anywhere in the world are prevented from spreading before they reach the United States.
Evidence has clearly shown that countries with seasonal influenza vaccination programs have had better and faster vaccine responses in each of the last two pandemics, when vaccines are especially life-saving. Effective global health partnerships are critical to American health, and diseases like bird flu know no borders. Investment in global health is vitally important for our health here at home. As my PIVI colleagues and I continue to monitor the bird flu virus, the lessons we learn here in the United States will help make our interconnected world safer as well.
