Question

Your friend told you that he is not going to get the flu vaccine this year because he got it last year and that it will certainly protect him this year. You tell him that, although that is the case with many vaccines, that is not the case with the flu vaccine. He asks you to explain the biology behind what you are saying. What do you tell him? (Hint: This is a question about viruses, not vaccines.)

Answer 1

Influenza virus are responsible for causing flu on every year. The virus evolves quickly and adapt changes due to antigenic drift(most common) and antigenic shift(occasionally). Mutations of the virus surface proteins occur.

The antigens are present on the surface of the viruses which triggers an immune response by producing antibodies . As they change every season ,they are not recognised by our immune system,so flu vaccine is produced newly every season and administrated every year.