Infantile paralysis was caused by a highly contagious virus called polio that invades the nervous system. About 60,000 Americans were infected with polio every year, and thousands were left permanently paralyzed in one or more limbs - including President Franklin D Roosevelt whose legs were paralyzed by polio. In the 1950s, the polio vaccine eradicated that awful disease.

I thought it important to explain this more fully, because so many people have stopped vaccinating their children, polio has returned to the United States.