H5N1 Avian Flu in the Americas: 2022-2026 Update | PAHO/WHO

The Pan American Health Organization (PAHO) continues to monitor the spread of avian influenza A(H5N1) across the Americas, with ongoing detections in both wild birds and poultry. As of March 9, 2026, influenza A(H5N1) has been identified in 37 mammalian species across two countries and 94 bird species across 11 countries and territories within the region. While detections in wild birds have shown a decline since mid-2025, outbreaks are increasingly concentrated in poultry and other domestic bird populations. This ongoing activity underscores the need for continued vigilance and biosecurity measures.

Avian Influenza A(H5N1) in the Americas: A Broad Picture

Since April 20, 2022, a total of 75 human infections with avian influenza A(H5N1) have been reported in five countries throughout the Americas, resulting in two fatalities. Importantly, there have been no additional confirmed human cases reported since the last PAHO/WHO epidemiological update on November 24, 2025. This relative stability in human cases doesn’t diminish the importance of continued surveillance, however, as the virus continues to circulate in animal populations.

Avian influenza, commonly known as bird flu, is a disease caused by influenza viruses that naturally spread among wild aquatic birds worldwide. These viruses can infect domestic poultry and, less frequently, mammals. Human infections are rare but can occur when people come into close contact with infected birds or contaminated environments. The current predominant strain circulating in the Americas is clade 2.3.4.4b, which has been active since 2021. PAHO’s recent reports highlight the challenges posed by this ongoing circulation to both biosecurity and food production across the region.

Mammalian and Avian Detections: Shifting Patterns

The detection of A(H5N1) in a wide range of mammalian species is a notable aspect of the current situation. While the virus primarily affects birds, its spillover into mammals – including both wild and domestic animals – raises concerns about potential further evolution and transmission dynamics. Canada and the United States have reported 77 outbreaks in mammals so far in 2025. The United States has also experienced significant outbreaks in dairy cattle, with over 1,000 herds affected across 18 states since March 2024. This detection in livestock, particularly dairy cattle, is prompting increased surveillance of both animal and human populations.

The shift towards more frequent outbreaks in poultry, as opposed to wild birds, suggests a change in the virus’s transmission patterns. This could be due to a number of factors, including increased movement of poultry, changes in biosecurity practices, or the virus adapting to better infect domestic bird species. The CDC is actively monitoring these trends and working with states to assess the risk.

Human Cases: Rare but Requiring Vigilance

While 75 human cases have been confirmed in the Americas since 2022, the overall number remains relatively low. The two fatalities occurred within this total. In 2025 alone, three cases were identified in the United States and one in Mexico. Notably, a case of influenza A(H5N5) was identified in the United States in November 2025 – the first globally reported human case caused by this specific viral subtype. The World Health Organization (WHO) has assessed the overall public health risk posed by A(H5) viruses as low, but acknowledges a low to moderate risk for individuals with occupational exposure.

It’s critical to understand that human infections with avian influenza are typically associated with direct or close contact with infected birds. The virus does not easily spread from person to person. However, the emergence of recent viral subtypes, like A(H5N5), necessitates ongoing monitoring for any changes in transmissibility.

Understanding the Risk: A(H5N1) and Beyond

The risk of contracting avian influenza remains low for the general public. However, individuals working with poultry, wildlife, or in related industries face a higher risk of exposure. The WHO currently assesses the risk to these groups as low to moderate. It’s crucial to remember that the risk assessment is based on the available evidence and is subject to change as the situation evolves. The detection of A(H5N5) in a human case, while not indicating widespread transmission, highlights the potential for the virus to mutate and adapt.

The term “clade” refers to a group of viruses that share a common ancestor. Clade 2.3.4.4b, the predominant strain in the Americas, has been circulating since 2021 and is characterized by its ability to cause outbreaks in both wild birds and poultry. Understanding the genetic characteristics of different clades is essential for tracking the virus’s evolution and assessing its potential impact on human health.

Public Health Response and Ongoing Surveillance

Public health authorities are employing a multi-faceted approach to address the ongoing avian influenza situation. This includes enhanced surveillance of both animal and human populations, rapid detection and response to outbreaks and the development of vaccines and antiviral medications. The CDC is utilizing its existing influenza surveillance systems to monitor for A(H5) activity in people, and data on human monitoring and testing are now reported monthly. USDA data on highly pathogenic avian influenza (HPAI) detections in animals are available on the USDA’s website.

The PAHO is also working with member states to strengthen biosecurity measures on poultry farms and to improve public awareness of the risks associated with avian influenza. This includes promoting safe handling practices for poultry and encouraging individuals to report any suspected cases of bird flu to local authorities.

What comes next: Continued surveillance remains paramount. PAHO and WHO are actively monitoring the virus’s evolution, tracking its spread, and assessing the effectiveness of current control measures. Regular updates will be provided as new information becomes available, and guidance will be adjusted as needed to protect public health. The focus will remain on early detection, rapid response, and preventing the further spread of the virus in both animal and human populations.