antigenic variation

Antigenic variation is a genetic mechanism that allows infectious agents to evade the host's immune system. This occurs through random genetic mutations, known as antigenic drift, which cause minor changes in the proteins (antigens) on the surface of the agent. These altered antigens are not fully recognized by existing antibodies, allowing the agent to replicate and spread.

This process is well-documented in influenza viruses, where changes in hemagglutinin (H) and neuraminidase (N) proteins lead to new strains that can cause epidemics or pandemics. Antigenic variation also occurs in viruses like HIV and rhinoviruses, and has been observed in parasitic protozoans such as trypanosomes, enabling them to survive by continually changing their surface coats to avoid host antibodies. This makes developing effective vaccines challenging.12