The correct answer is Antigenic Drift.
What is Antigen?
A chemical agent that can injure living things and trigger an immune response is referred to as an antigen. The targeted antibody is made in opposition to the immune response.
Different defense mechanisms have been developed by the antigens to shield them from the host's immune system. The most frequent modification that can happen to viruses and aids the antigen in defending itself by altering its genetic makeup is known as the antigenic shift. For the viruses, there are no antiviral medications available.
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