antigenic drift
Antigenic drift is a process where viruses, particularly influenza, gradually change their surface proteins over time due to small mutations during replication. These changes can alter how the immune system recognizes the virus, making it harder for the body to defend against it. As a result, even if you’ve had a virus before or been vaccinated, the virus can still infect you because it looks different enough to evade your immune response. This ongoing change is why annual flu vaccines are necessary, as they aim to match the circulating virus strains.
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Antigenic drift is a gradual process through which viruses, especially influenza, change over time due to small mutations in their genetic material. These changes alter the virus's surface proteins, called antigens, which are recognized by the immune system. As a result, the immune system may no longer recognize the virus effectively, making it easier for the virus to infect individuals who have been previously exposed or vaccinated. This constant evolution is why vaccines need regular updates to remain effective against circulating virus strains.