Antigen may be defined as the chemical that has the ability to evoke the and immune response and can harm the living organisms. The specific antibody are produced against the immune response.
The antigens has evolved different mechanisms to prevent themselves from them the immune system of the host. The antigenic shift is the most common change that might occur in viruses that helps the antigen to protect itself by changing its genetic material. No anti viral drugs are available for the viruses.
