What were the differences between the polio shot (IPV) and polio drops (OPV)?
Each vaccine recommended for use against polio had its advantages and disadvantages. The advantage of the OPV was that it was almost 100 percent effective at preventing polio. Also, because the vaccine virus was present in the stool, about 25 percent of people who came in contact with someone who was immunized, would also be immunized (this is called contact immunity). In the early 1960s, when immunization rates in this country were low, contact immunity was an important feature of OPV. However, despite OPV’s 40 years of success, there was an extremely rare but frighteningly dangerous side effect: permanent paralysis. Paralysis caused by OPV occurred in about one of every 750,000 people after taking the first doses of the vaccine. Since 1979, the time when natural polio was eliminated from the United States, OPV caused about six to eight cases of paralysis each year. The IPV form, now recommended by the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediat
