The flu shot only provides short-term effects since the virus mutates frequently so we need it every year.
We understand that it might not be as convenient as other vaccines like the ones for mumps or whooping cough that you get once and then can forget about, but it is important to get the flu vaccine every year, hence the name “seasonal influenza”. The reason for this is because our body’s immunity to the flu fluctuates. Another issue with the flu is that it is always mutating and, as a result, different strains are more prominent each year.
For instance, there has been a lot of talk in the past about H1N1. This is just one strain of the flu virus. The different strains infect people at different times.
