There are two types of vaccinations for polio (also called poliomyelitis). One type is an inactivated vaccine, which contains no live poliovirus. It is given as a shot in the arm or leg, depending on the person's age. The other type is the oral vaccination, which contains live but weakened poliovirus.
Although both types are quite effective in preventing the disease, the oral vaccine does pose a slight risk of a rare but serious condition known as vaccine-associated paralytic poliomyelitis. Therefore, its use in the United States has been discontinued -- an enhanced-potency inactivated polio vaccine is now used instead. The oral vaccine is still used for polio prevention in many other parts of the world.
Most people should get vaccinated when they are children (adults can also receive the vaccine if necessary). Polio vaccination usually consists of four doses, the last of which is a "booster shot."
(Click Polio Vaccine for more details, including specific dosing schedules for adults and children.)