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        Influenza (Flu)
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              For Everyone
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    How CDC Classifies Flu Severity each Season in the United States Information for Laboratories Understanding Influenza Viruses WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza Viral Genomic Sequencing Infrastructure View All
September 9, 2024
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  Understanding Influenza Viruses
          Purpose
          This page provides information on influenza viruses, including their antigens, how they can change through "drift" and "shift," the process of influenza virus genome sequencing and genetic characterization, human serology and flu, as well as advanced molecular detection (AMD) and influenza.
        Antigenic Characterization
        “Antigens” are molecular structures on the surface of viruses that are recognized by the immune system and are capable of triggering one kind of immune response known as antibody production. Two proteins (hemagglutinin and neuraminidase) on the surface of influenza viruses contain the major antigens targeted by antibodies. Antigenic characterization refers to the analysis of antigenic properties of viruses to examine their relatedness. CDC antigenically characterizes viruses to monitor for changes in circulating viruses and to compare how similar these viruses are to those included in flu vaccines.
          Keep Reading: Antigenic Characterization
        How Flu Viruses Can Change: "Drift" and "Shift"
        One way influenza viruses change is called "antigenic drift." Drift consists of small changes (or mutations) in the genes of influenza viruses that can lead to changes in the surface proteins of the virus, HA (hemagglutinin) and NA (neuraminidase).
        Another type of change is called "antigenic shift." Shift is an abrupt, major change in an influenza A virus, resulting in new HA and/or new HA and NA proteins in influenza viruses that infect humans.
          Keep Reading: How Flu Viruses Can Change:
        Influenza Virus Genome Sequencing and Genetic Characterization
        Genome sequencing is a process that determines the order, or sequence, of the nucleotides (i.e., A, C, G and T/U) in each of the genes present in the virus’s genome. The process of comparing genetic sequences is called genetic characterization.
          Keep Reading: Influenza Virus Genome Sequencing and Genetic Characterization
        Human Serology & Flu
        Serology is the scientific study of blood to look at the response of the immune system to vaccination or infections with pathogens, like influenza viruses. To improve seasonal flu vaccines and prepare against future pandemics, CDC’s Influenza Division conducts a wide range of laboratory activities involving human serology.
          Keep Reading: Human Serology & Flu
        Advanced Molecular Detection (AMD) and Influenza
        CDC is using next-generation gene sequencing tools to analyze influenza viruses as part of CDC's Advanced Molecular Detection (AMD) initiative. The technology allows CDC to study more influenza viruses faster and in more detail than ever before. AMD technology uses genomic sequencing, high-performance computing, and epidemiology to study pathogens and improve disease detection. CDC is using the technology to monitor genetic changes in influenza viruses in order to better understand and improve the effectiveness of influenza vaccines.
          Keep Reading: Advanced Molecular Detection (AMD) and Influenza
        On This Page
            * Antigenic Characterization
            * How Flu Viruses Can Change: "Drift" and "Shift"
            * Influenza Virus Genome Sequencing and Genetic Characterization
            * Human Serology & Flu
            * Advanced Molecular Detection (AMD) and Influenza
          Related PagesHow Flu Viruses Can Change: "Drift" and "Shift"
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            * How Flu Viruses Can Change: "Drift" and "Shift"
            * Antigenic Characterization
            * Influenza Virus Genome Sequencing and Genetic Characterization
        * 
            * Human Serology & Flu
            * Information for Laboratories
        * 
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    How Flu Viruses Can Change: "Drift" and "Shift"
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  September 9, 2024
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      Related PagesHow Flu Viruses Can Change: "Drift" and "Shift"
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        * How Flu Viruses Can Change: "Drift" and "Shift"
        * Antigenic Characterization
        * Influenza Virus Genome Sequencing and Genetic Characterization
    * 
        * Human Serology & Flu
        * Information for Laboratories
    * 
      View All Influenza (Flu)
  Back to Top
    Influenza (Flu)
    Influenza (flu) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs.
    View All
        For Everyone
          * About
          * Signs and Symptoms
          * Causes and Spread
          * Flu Complications and People at Higher Risk
          * Prevention
          * Vaccine Basics
          * Diagnosis
          * Flu Treatment
          * View all
          Health Care Providers
            * Clinical Guidance
            * Clinical Signs and Symptoms of Influenza
            * Guidance for Influenza Vaccination
            * View All
          Public Health
            * How CDC Classifies Flu Severity each Season in the United States
            * Information for Laboratories
            * Understanding Influenza Viruses
            * View All
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