Antigenic drift refers to mutations in the influenzavirus over time. Such mutations occur almost yearly in the influenza virus. For this reason, vaccination is required on a yearly basis. In influenza mutations happen frequently because the virus is highly unstable and has no way of checking its DNA for errors. Even a tiny error in the DNA is permanent. Antigenic drift has been responsible for large outbreaks in the past, like the outbreak of influenza A Fujian(H3N2) in the 2003 - 2004 flu season. All influenza viruses experience some form of antigenic drift, but it's most pronounced in the influenza A virus. Antigenic drift is not the same as antigenic shift, which is a major change in the surface proteins on the virus.
Antigenicdrift has been responsible for heavier than normal flu seasons in the past, like the outbreak of influenza A Fujian(H3N2) in the 2003 - 2004 flu season.
Antigenicdrift is not the same as antigenic shift, which is a major change in the surface proteins on the virus.
Antigenic shift is the process by which two different strains of influenza combine to form a new subtype having a mixture of the surface antigens of the two original strains.
Antigenic shift is contrasted with antigenicdrift, which is the natural mutation over time of known strains of influenza (or other things, in a more general sense) to evade the immune system.
Antigenicdrift occurs in all types of influenza including influenza A, B and C. Antigenic shift, however, occurs only in influenza A because it infects more than just humans.
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