Antigenic drift in Influenza virus is the ability of virus to produce point mutations in the genetic material. Antigenic drift alters the virulence of Influenza virus. When antigenic drift occurs, the body’s immune system fails to recognize the newer version of Influenza virus. The antibodies exist for the pre-drift version which are ineffective against the newer version. Thus, immune system fails to prevent the sickness as it is easier for this virus to attack and infect the same individual more than once because of drift.