H5N1 Bird Flu Poses Low Risk to the Public

CDC Update

Right now, the H5N1 bird flu situation is primarily an animal health issue. The U.S. Department of Interior and USDA APHIS are the lead federal agencies for this situation. They are respectively responsible for outbreak investigation and control of bird flu in wild birds and in domestic birds (poultry). USDA has publicly posted the genetic sequences of several of the recently detected U.S. H5N1 bird flu viruses. These viruses are from clade 2.3.4.4b1, which is the most common H5N1 bird flu virus worldwide at this time. Comparing information about these newer viruses to previously circulating H5N1 bird flu viruses helps inform the human health risk assessment.

Ancestors of the H5N1 bird flu viruses infecting wild birds and poultry in the U.S. beginning in 2021 first emerged in southern China in 1996 and caused large poultry outbreaks in Hong Kong in 1997, which resulted in 18 human infections. The bird outbreak was controlled, but H5N1 bird flu viruses re-surfaced in 2003 to spread widely in birds throughout Asia, and later in Africa, Europe, and the Middle East, causing poultry outbreaks and sporadic human infections. Related H5N1 bird flu viruses were even found in wild birds and poultry in the U.S. and Canada during 2014 and 2015, causing large poultry outbreaks, but then they disappeared. Since 2003, the World Health Organization (WHO), has received reports from 19 countries of more than 860 human infections with H5N1 bird flu viruses, with about 53 percent of those resulting in death. CDC has spent many years studying the properties of H5N1 viruses over the years.

Information on Current H5N1 Viruses

Current H5N1 bird flu viruses were first identified in Europe during the fall of 2020 and spread across Europe and into Africa, the Middle East and Asia, becoming the predominant subtype globally by fall of 2021. These viruses have been spreading in wild birds in much of the world and causing sporadic poultry infections and poultry outbreaks in many countries, most recently the United States. CDC has been comparing the properties of current H5N1 bird flu viruses to past H5N1 bird flu viruses and has found that current H5N1 bird flu viruses detected in the U.S. during late 2021 and 2022 are different from earlier H5N1 bird flu viruses. So far, current H5N1 bird flu viruses lack changes seen in the past that have been associated with viruses spreading easily among poultry, infecting people more easily, and causing severe illness in people. There is little information about the spectrum of illness that could result from human infections with current H5N1 bird flu viruses. At this time, only one human infection with current H5N1 bird flu viruses has been reported. That infection was found in January 2022 in a person in the United Kingdom who did not have any symptoms and who raised birds that became infected with H5N1 bird flu viruses. No human infections with H5N1 bird flu viruses have ever been identified in the U.S. Based on information at this time, it may be that current H5N1 viruses offer less of a risk to human health than earlier H5N1 viruses.

Based on available genetic sequence data of current H5N1 bird flu viruses, CDC has determined:

• An H5 candidate vaccine virus (CVV) recently produced by CDC is nearly identical to the HA of recently detected H5N1 viruses in birds and could be used to produce a vaccine for people, if needed.
• These viruses are susceptible to currently available antiviral medications used to treat seasonal flu.
• 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.

What is CDC Doing?

• Because flu viruses are constantly changing, CDC will continue to monitor these viruses to look for genetic or epidemiologic changes suggesting they might spread more easily to and between people, and cause serious illness in people, or for changes that suggest reduced susceptibility to antivirals, as well as changes in the virus that might mean a new CVV should be developed.
• 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 have occurred. If human infections with H5N1 bird flu virus are identified, CDC will help with surveillance, contact tracing, and other steps to monitor for and reduce spread in affected jurisdictions. At this time, more than 140 people in the U.S. who have had H5N1 exposures with infected birds/poultry have been or are being monitored for symptoms and no cases of H5N1 infection have been found.
• CDC is conducting additional laboratory work to further characterize current H5N1 bird flu viruses.
• CDC is providing guidance including recommendations for personal protective equipment and information for people exposed to birds infected with avian influenza viruses and guidance for testing and treatment. A review of these guidance documents for any needed updates is ongoing.

What Might Happen

Given past human infections with bird flu viruses resulting from close contact with infected birds/poultry, sporadic human infections with current H5N1 bird flu viruses would not be surprising, especially among people with exposures who may not be taking recommended precautions (like wearing personal protective equipment, for example). Sporadic infections like that would not change CDC’s risk assessment. However, identification of multiple instances of H5N1 bird flu viruses spreading from birds to people, or of changes in the virus associated with adaptation to mammals, would raise CDC’s risk assessment. These changes could indicate the virus is adapting to spread more readily from birds to people. If limited, non-sustained human-to-human spread with this virus were to occur, that also 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.

What To Do

As a general precaution, people should avoid direct contact with wild birds and observe them only from a distance, if possible. Wild birds can be infected with bird flu viruses without appearing sick. If possible, avoid contact with poultry that appear ill or have died. Avoid contact with surfaces that appear to be contaminated with feces from wild or domestic birds, if possible. CDC has information about precautions to take with wild birds. CDC also has guidance for specific groups of people with exposure to poultry, including poultry workers and people responding to poultry outbreaks. If you must handle wild birds or sick or dead poultry, minimize direct contact by wearing gloves and wash your hands with soap and water after touching birds. If available, wear respiratory protection such as a medical facemask. Change your clothing before contact with healthy domestic poultry and birds after handling wild birds, and discard the gloves and facemask, and then wash your hands with soap and water. Additional information is available at Information for People Exposed to Birds Infected with Avian Influenza Viruses of Public Health Concern. 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 H5N1 bird flu viruses.

Human Infections with Bird Flu Viruses

Infected birds shed bird flu viruses in their saliva, mucous and feces. Bird flu infections among people are rare; however, human infections can happen when enough virus gets into a person's eyes, nose, or mouth, or is inhaled. People with close or lengthy unprotected contact (not wearing respiratory protection or eye protection) with infected birds or places that sick birds or their mucous, saliva, or feces have touched, may be at greater risk of bird flu virus infection. Illnesses in people from bird flu 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 bird flu viruses from one infected person to a close contact is very rare, and when it has happened, it has not led to continued spread among people.