What does antigenic shift refer to?

Antigenic shift refers to an abrupt major change in a virus, particularly in the context of influenza viruses. This phenomenon occurs when two different strains of a virus infect the same host cell and exchange genetic material. As a result, a new subtype of the virus is formed. This can lead to significant changes in the surface antigens of the virus, which are the components recognized by the immune system.

The consequence of antigenic shift is that the human immune system may no longer recognize the virus, leading to outbreaks or pandemics because the population lacks immunity to the newly formed virus. This is distinct from antigenic drift, which involves small, gradual changes that occur over time in the virus's genetic makeup. The abrupt nature of antigenic shift and its potential to create entirely new virus strains is what distinguishes it as a significant factor in viral evolution and public health concerns.