MODEL RELEASED. Polio vaccination. A nurse gives oral polio vaccine to a 4-year-old boy, watched by his mother. This vaccine contains harmless, live strains of all three types of polio virus. The attenuated viruses stimulate the patient's immune system to produce antibodies against polio, giving immunity. Polio (poliomyelitis) is an infectious disease that can permanently damage parts of the nervous system, sometimes causing paralysis. Children are vaccinated at 3, 5 and 9 months, and receive a booster dose prior to starting school.