Antigenic drift refers to the gradual and continuous process of genetic mutation in the antigens of viruses, particularly in the surface proteins such as hemagglutinin and neuraminidase of the influenza virus. These small changes accumulate over time, allowing the virus to evade the host's immune system. This process is a key factor in the seasonal variations of influenza outbreaks and necessitates the annual update of the influenza vaccine to match the circulating strains.
