Updated: H5N1 Bird Flu Virus in U.S. Wild Birds and Poultry Poses a Low Risk to the Public
February 22, 2022—Highly pathogenic avian influenza (HPAI) A(H5N1) viruses have been detected in U.S. wild birds and commercial and domestic poultry, according to the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspective Service (APHIS). Avian influenza is a disease of birds caused by infection with avian influenza A viruses (bird flu viruses). However, avian influenza A virus infection of people is rare. CDC believes that the current risk to the general public’s health from HPAI A(H5N1) virus in the U.S. is low. However, some people may be at a higher risk of infection than others based on their exposures to infected birds, particularly poultry workers. There is existing federal guidance related to bird flu exposures for different groups of people, including hunters [ 297 KB, 2 pages], poultry producers, responders to bird flu outbreaks in birds [353 KB, 18 pages], the general public, as well as health care providers. While these bird flu outbreaks are largely an animal health issue, CDC is working closely with USDA to monitor for potential human infections and taking other routine preparedness and prevention measures in anticipation of possible human infections.
On the animal health side, the U.S. Department of Interior and USDA are the lead federal departments for outbreak investigation and control of bird flu in wild birds, and USDA APHIS is the lead agency for such activities in domestic birds. As a reminder, it is safe to eat properly handled and cooked poultry and poultry products in the United States. The proper handling and cooking of poultry and eggs to an internal temperature of 165˚F kills bacteria and viruses, including HPAI A(H5N1) viruses.
Wild birds can be infected with HPAI A(H5N1) viruses without showing symptoms, but these viruses can cause illness and death in domestic poultry. USDA has publicly posted genetic sequencing for several of the recently detected U.S. HPAI A(H5N1) viruses. These viruses are from clade 188.8.131.52b*, which is the predominant HPAI A(H5N1) virus worldwide at this time. Ancestors of these HPAI A(H5N1) viruses first emerged in southern China and led to large poultry outbreaks in Hong Kong in 1997, which resulted in 18 human infections. The outbreak was controlled, but the HPAI A(H5N1) virus re-surfaced in 2003 to spread widely in birds throughout Asia, and later in Africa, Europe, and the Middle East.
Human Infections with Avian Influenza A viruses
Infected birds shed avian influenza A viruses in their saliva, mucous and feces. Human infections with bird flu viruses can happen when enough virus gets into a person’s eyes, nose, or mouth, or is inhaled. People with close or prolonged unprotected contact with infected birds or virus contaminated environments may be at greater risk of bird flu virus infection. Illnesses in humans from avian influenza A virus infections have ranged from mild (e.g., eye infection, upper respiratory symptoms) to severe illness (e.g., pneumonia) that can result in death. The spread of avian influenza A viruses from one infected person to a close contact is very rare, and when it has happened, it has not led to sustained spread among people. Since 2003, 19 countries have reported more than 860 total human infections with HPAI A(H5N1) viruses to the World Health Organization (WHO), with about 53 percent of those resulting in death. The most recent human infection with HPAI A(H5N1) virus was reported in the United Kingdom in January 2022 in association with exposure to domestically kept infected birds. No human infections with highly pathogenic avian influenza A viruses** have been detected to date in the United States; however, sporadic human infections with HPAI A(H5N1) bird flu viruses resulting from close contact with infected birds/poultry would not be surprising given past human infections that have occurred sporadically in other countries. CDC will work with state partners to minimize the possibility of human infection and, if one occurs, minimize the risk to others.
What is CDC Doing?
Based on available gene sequencing, CDC has determined:
- CDC has produced a candidate vaccine virus (CVV) that is nearly identical to the recently detected HPAI A(H5N1) viruses in birds that could be used to produce a vaccine for people, if needed.
- These viruses are susceptible to currently available antiviral medications used to treat influenza.
- These viruses can be detected using CDC’s diagnostic tools for seasonal influenza viruses which are used at more than 100 public health laboratories in all 50 U.S. states and internationally as well.
CDC is working with USDA and state public health partners to monitor for potential infections in exposed persons in the states where H5N1 bird flu virus detections in poultry and backyard flocks have occurred. If human infections with H5N1 bird flu virus are identified, CDC will assist with surveillance, contact tracing, and steps to reduce further spread, in the affected jurisdictions. CDC will also alert clinicians and other health professionals through clinician outreach networks. CDC has guidance documents including recommendations for personal protective equipment and information for people exposed to birds infected with avian influenza A viruses and guidance for testing and treatment of suspected cases to prevent severe illness and transmission to other people. CDC is currently reviewing and updating this guidance as needed.
Risk Assessment Ongoing
CDC will continue its ongoing assessment of the risk posed by these viruses, including conducting laboratory experiments to further characterize the HPAI A(H5N1) virus. For example, continuing to look for genetic markers that might result in greater transmissibility to and between people or suggest reduced susceptibility to antivirals, as well as changes in the virus that might require the development of a new CVV. While sporadic bird-to-human infections would not raise the public health risk assessment, identification of multiple instances of HPAI A(H5N1) virus spread from birds to people, or of markers of mammalian adaptation in the virus, would raise CDC’s risk assessment. These changes could indicate the virus is adapting to spread more readily from birds to people. If human-to-human spread with this virus were to occur, that would raise the public health threat because it could mean the virus is adapting to spread better between people. Note that sustained human-to-human spread is needed for a pandemic to occur.
*Clades are explained on CDC’s Avian Influenza Current Situation Summary webpage in the section titled “Classification of Avian Influenza A viruses.”
**There have been four human infections with low pathogenic avian influenza A viruses identified in the United States since 2002. The designation of pathogenicity is related to severity of illness in poultry, not illness in people.