OPV is highly effective in producing immunity to poliovirus. A single dose of OPV produces immunity in approximately 50 percent of recipients. Three doses of OPV will produce immunity to all three poliovirus types in more than 95 percent of recipients. As with other live-virus vaccines, immunity from OPV is probably life-long.
There are two general polio vaccine types. One type is inactivated polio vaccine (IPV), meaning that the vaccine contains no live poliovirus. The other type is live OPV, which contains live but weakened poliovirus.
Until recently, OPV was recommended for most children in the United States. Because OPV helped rid the United States of polio (and because it is less expensive than the newer inactivated polio vaccine), it is still used in many parts of the world.
Both vaccines give immunity to polio, but OPV is better at keeping the disease from spreading to other people. However, for a few people (about one in 2.4 million), OPV actually causes polio (known as vaccine-associated paralytic polio). Since the risk of getting polio in the United States is now extremely low, experts believe that using OPV is no longer worth the slight risk, except in limited circumstances, which your doctor can describe. The polio shot (inactivated polio vaccine) does not cause polio.
(Click Polio Vaccine to learn more about the inactivated polio vaccine.)
Vaccine-associated paralytic poliomyelitis is a rare adverse reaction that can come from the oral polio vaccine. It is caused by vaccine-derived poliovirus. One case of vaccine-associated paralytic poliomyelitis occurred for every 2 to 3 million doses of OPV administered. This resulted in 8 to 10 cases of vaccine-associated paralytic poliomyelitis each year in the United States.
From 1980 through 1999, vaccine-associated paralytic poliomyelitis accounted for 95 percent of all cases of paralytic poliomyelitis reported in the United States.
(Click Vaccine-Associated Paralytic Poliomyelitis to learn more about this rare but serious reaction to oral polio vaccine.)