From this Age of Autism post:
1) The polio epidemic wasn't that bad (said by someone who actually had polio!)
2) Mother Nature intends for us to catch infectious diseases. Everything we do to avoid catching them merely forces bacteria and viruses to evolve into stronger and stronger strains, until eventually we'll all be catching them again, except we'll be worse off because they'll have developed into super bacteria and viruses. So, in the long run, it's better to avoid using vaccines and antibiotics and for humanity to simply take its lumps.