Influenza A viruses are a subtype of the influenza virus that primarily infects birds and some mammals, including humans. These viruses are known for their ability to rapidly mutate and evolve, leading to the emergence of new strains that can cause seasonal outbreaks and occasionally pandemics. Influenza A viruses are classified based on the two surface proteins they possess: hemagglutinin (HA) and neuraminidase (NA). These viruses are responsible for the flu, a contagious respiratory illness that can range from mild to severe, and can lead to complications such as pneumonia. Understanding the genetics, transmission, and immune response to influenza A viruses is essential for developing effective vaccines and therapies to prevent and control outbreaks.