Vaccination against many contageous diseases is a marvel of modern medicine. Even adults can benefit. Here's an exerpt from the interview Vaccines: Not Just for Babies:
Medscape: There is a lot of skepticism about the utility and safety of vaccine among the general public. Can you describe a recent success story?
Dr. Fisher: One of the most remarkable things that's happened recently involves the introduction of the pneumococcal conjugate vaccine in 2000. Within a year, there was a dramatic drop in disease caused by the 7 serogroups in that vaccine. Not only was there a drop in children who were immunized, there was a drop in their siblings, parents, and grandparents, which was totally surprising. It sounded like magic.
What happened was that the vaccines got rid of carriers of the organism. About two thirds of children carry pneumococcus in their airway. If you can get the strains most likely to cause disease out of the children, they don't transmit it to their parents and grandparents.