The influenza A virus is a type of virus that causes seasonal flu outbreaks in humans and can also infect animals, particularly birds and pigs. It is known for its ability to mutate rapidly, leading to new strains that can evade the immune system. This characteristic makes it a significant concern for public health. Influenza A is classified into subtypes based on two proteins on its surface: hemagglutinin (H) and neuraminidase (N). For example, the H1N1 strain gained worldwide attention during the 2009 pandemic. Vaccines are developed annually to protect against the most common strains of the virus.