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Avian Influenza (Bird Flu) Research

Why does CDC conduct research on bird flu viruses?

Although bird flu viruses mainly infect birds, these viruses can sometimes infect people and cause illness. Flu viruses constantly change (see antigenic drift and shift) and sometimes these changes result in the emergence of a novel (new) flu virus that can easily infect and spread between people. When this happens, a pandemic can occur. CDC Influenza Division is a World Health Organization (WHO) Collaborating Center. In this role, CDC conducts surveillance of circulating flu viruses to make informed decisions on the selection of viruses for use in creating vaccines against viruses with pandemic potential. Because of the possible threat bird flu viruses pose to human health, CDC also conducts research to learn more about these viruses, for example, where they spread, how they spread, and what kinds of disease they cause. This information can help scientists better understand the risk these viruses pose to human health and can help support development of tools and strategies for prevention and treatment.

In recent years, two bird flu viruses have caused the most human infections: highly pathogenic Asian lineage avian influenza (HPAI) H5N1 and Asian lineage H7N9 viruses (Note: the term “highly pathogenic” refers to the severity of disease that these viruses cause in birds). These two viruses have caused severe illness and death in humans.

For these reasons, CDC has focused considerable resources and time on monitoring human infections with and changes in these and other bird flu viruses, as well as developing vaccine viruses and testing antiviral drugs to prevent or treat human infections with them.

What is the purpose of this research?

CDC conducts laboratory research on bird flu viruses for important public health reasons, including but not limited to the following:

  • to develop viruses for use in vaccines as part of pandemic preparedness efforts;
  • to test to see if bird flu viruses are susceptible (sensitive) or resistant to existing flu antiviral drugs, and to monitor for ongoing changes that might indicate these viruses are becoming resistant;
  • to develop diagnostic tests and test materials that can accurately and reliably detect infections with specific bird flu viruses, such as Asian H5N1 and Asian H7N9;
  • to assess existing human immunity to circulating bird flu viruses and to determine whether people’s previous vaccinations or exposures to other flu viruses provides cross-protection against newer bird flu viruses.
  • to better understand properties of bird flu viruses and changes in bird flu viruses ( mutations) that could cause such viruses to infect people more easily, cause more severe disease, or spread in a sustained and efficient manner among people or other mammals;
  • to track globally where bird flu viruses are causing illness in people so that appropriate public health precautions and actions can be taken to minimize risks to the public’s health in those areas.

What research does CDC conduct on bird flu viruses?

CDC conducts laboratory tests on bird flu viruses including, but not limited to the following: antigenic characterization, antiviral resistance, genetic characterization, serology and assessment of bird flu viruses’ ability to cause disease and spread in animal models. An explanation of this research and its public health purpose is provided below.

Genetic Characterization

Genetic characterization – as it applies to bird flu research – is the study of the genes of a bird flu virus through a laboratory process known as “genome sequencing.” Through genome sequencing, researchers can determine the order and structure of the amino acids that bind together to form the proteins of a flu virus. Comparing the order of amino acids in one sequence to other sequences can reveal variations that might impact characteristics of the flu virus. For example, the ordering of these amino acids can affect factors such as how well a virus replicates during infection, how well it transmits between hosts, or its susceptibility to vaccines and antiviral drugs. Flu researchers use genetic characterization to better understand these markers and to assess the risk these viruses pose to public health. All flu virus samples submitted to CDC undergo genetic sequencing as a first step in the process of studying the virus.

Antigenic Characterization

“Antigenic characterization” is the analysis of a flu virus’ surface features using antibodies. CDC researchers determine a flu virus’ antigenic (immune) properties to help assess how related different flu viruses are to each other. CDC flu laboratorians conduct antigenic characterization as part of global flu surveillance efforts to measure possible changes in circulating bird flu viruses. Antigenic characterization data help CDC experts determine if existing bird flu vaccines that have been stockpiled in the event of a pandemic would be expected to provide protection against circulating bird flu viruses or if new vaccine viruses should be developed. In some circumstances, CDC may prepare viruses in advance that vaccine manufacturers can use to produce a vaccine in the future, if needed. The main test used to conduct antigenic characterization is the Hemagglutination Inhibition Assay (HI Test). CDC primarily conducts antigenic characterization on bird flu H5, H7, and H9 viruses, but may test other types of bird flu viruses that pose a risk to humans. More information on antigenic characterization is available on CDC’s flu antigenic characterization page.

Antiviral Resistance Testing

Virus samples are tested to determine if they are resistant to any of the FDA-approved flu antiviral drugs. This information helps shape public health policy recommendations on the use of flu antiviral medications. CDC currently recommends use of the neuraminidase inhibitor class of antiviral drugs to prevent and treat flu illness in the United States. The neuraminidase inhibitors are drugs that are designed to bind to the neuraminidase protein on the surface of a flu virus to prevent the virus from replicating in the host. (More information about flu antiviral drugs is available at Treatment – Antiviral Drugs.) Antiviral resistance testing includes using a specific functional assay, the neuraminidase inhibition (NI) assay, to see whether virus replication is inhibited by the presence of the neuraminidase drugs.


Serology is the study of blood serum. Serum contains antibodies, which are proteins that are produced by the body in response to infection or vaccination. Antibodies play an essential role in protection against flu viruses. CDC’s flu serology research involves the study of antibodies in human populations to better understand whether people have any existing protection against bird flu viruses. These studies can tell public health officials whether people in the study population are susceptible to infection with a particular virus or if they have existing immune protection against infection. This information is important for determining a virus’ pandemic potential or ability to spread through a population. In addition, serology is used to determine whether vaccines developed against bird flu viruses are likely to offer adequate protection and whether this protection is likely to be effective against newly emerging bird flu viruses.

Animal testing

CDC conducts animal studies using bird flu viruses to better understand these viruses, such as how transmissible they are in mammals, their disease severity and disease characteristics, and to test the efficacy of vaccines and other pharmaceutical interventions against them.

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How has CDC research helped to improve testing for bird flu viruses?

CDC research has strengthened the ability of the United States and foreign countries to detect bird flu viruses. In February 2006 and September 2008, the U.S. Food and Drug Administration (FDA) cleared laboratory tests researched and developed by CDC to identify Asian H5N1 bird flu virus in human respiratory specimens to aid in the diagnosis of suspected cases. CDC has since expanded its test kits to detect other bird flu viruses, such as Asian H7N9 bird flu virus, which began causing human infections in China in 2013. CDC’s bird flu test kits have been made available to state public health laboratories and have been shared globally with the Collaborating Centers of the World Health Organization and international influenza testing centers.

What is “dual use research of concern (DURC)”?

CDC only conducts bird flu research to benefit society. Some types of bird flu research that are beneficial to society also fall into a category called “dual use research of concern” (DURC). DURC is defined as life sciences research that, based on current understanding, can be reasonably anticipated to provide knowledge, information, products, or technologies that could be directly misapplied to pose a significant threat with broad potential consequences to public health and safety, agricultural crops and other plants, animals, the environment, materiel, or national security. DURC is a subset of research called “dual use research” (DUR). DUR is defined as research that is beneficial to society that could also pose risks to health or security if used malevolently. More information about DURC can be found at Dual Use Research of Concern and Bird Flu: Questions & Answers.
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