How were the “inactivated” and “oral” polio virus vaccines made?
OPV was made by weakening the three strains of polio virus that caused disease by growing them in monkey kidney cells. Polio virus that was grown in these cells was so “weakened” that, after it was swallowed, it induced an immune response but didn’t cause disease. OPV induced antibodies in the intestines and, therefore, because polio enters the body through the intestines, provided a “first line” of defense against polio. IPV, unlike OPV, cannot reproduce itself (or replicate) and, therefore, cannot possibly revert back to natural polio. To make IPV, polio virus is purified and killed with a chemical (formaldehyde). IPV elicits antibodies in the bloodstream, not the intestines. It prevents the virus from traveling through the blood to the brain or spinal cord, thereby preventing paralysis. In a sense, because the vaccine induces antibodies in the bloodstream, and not the intestines, IPV induces a “second line” of defense against infection.
