Immunization is the process through which an individual is protected against a virus. Depending upon the vaccine, it can often grant full immunity from the virus. Since the time a polio vaccine was first created and dispensed, most individuals now have immune systems equipped with the necessary strength to fight off the poliovirus, and polio cases have dramatically decreased.

Intercostal expansion is an action whereby intercostal muscles expand the ribs upward and outward to likewise expand the thoracic cavity, in order to draw air into the lungs. Polio patients may experience paralysis of the intercostal muscles, which leads to respiratory difficulties; increased respiratory difficulties often required the patient to spend time in an iron lung, which could breathe for the patient until they gained enough strength to do so on their own.

An iron lung is a tube-shaped respirator that encloses a patient’s entire body save for their head and controls air pressure in the enclosed space to facilitate breathing. The metal machine is attached to massive bellows that emit strong gusts of air in and out, thereby expanding and contracting a patient’s lungs. In polio patients, the machine is used to assist with breathing when the severity of their muscle weakness makes independent breathing impossible.