antigenic shift

Antigenic shift is a significant change in the viruses that cause diseases, like influenza. It occurs when two different strains of a virus infect the same cell and exchange genetic material, leading to a new strain. This new virus can have different surface proteins, making it harder for the immune system to recognize and fight it, even in people who have been vaccinated or previously infected. This process can lead to pandemics, as the population may have little or no immunity to the newly formed virus. Essentially, it's a major transformation that can change how the virus behaves.