Does vaccination make the immune system "lazy"? I was having this discussion with a friend over vaccination against the flu. Although he agrees that vaccination against almost all diseases is necessary, he said that flu shots are not. He argued that the immune system is like the muscular system. It constantly goes through training. Flu shots deprive the body from "natural exercise" since, he believes, we need to train our immune system by getting "the right amount" of the real viruses from the environment. In other words, if we do too much vaccination (and flu shots are "too much") we make our immune system lazy. Is this true? I know that there is a difference between natural immunization and vaccination, is it correct though to say that the latter makes your immune system lazy? I was under the impression that vaccination's function resembles more the way we learn and memory and less the musclar system which can get lazy.

Contrary to many beliefs our immune system needs no "training". It is permanently active and confronted with dozens to hundreds of antigens in our food, from dust we inhale and so on. This all happens to protect our body from the environment and the immune system is pretty efficient with that and certainly it is not getting lazy.

By vaccinating against a certain disease, you generate immunogenic memory against this disease. When you then get exposed to the disease, this memory helps to speed up the immunogenic reaction against the disease - ideally you are not getting sick, in some cases the progression of the disease is much milder.

Further reading:

* Wikipedia on adaptive immunity
* The front line of host defense from Janeway at the NCBI Bookshelf