History of Polio Vaccines

• Polio vaccination successfully eradicated the disease from the United States. Before immunization, epidemics occurred regularly every spring and fall. In the U.S. in 1952, paralytic polio cases peaked at 21,000, according to the Centers for Disease Control and Prevention (CDC). The inactivated polio vaccine (IPV) was licensed in 1955 and the oral polio vaccine (OPV) became available in 1963. Mass immunization programs dramatically reduced the number of polio cases. By 1960, 2,525 paralytic cases were reported. Five years later, in 1965, the number of paralytic cases dropped to 61. No cases of natural polio have occurred in the U.S. since 1979. The only cases of natural polio occurring in the U.S. are now caused by virus carried by travelers from countries where polio remains endemic.
  
  

Types of Polio Vaccines

• IPV, an injectable vaccine, is manufactured using the shell of the poliovirus, which is sufficient to confer immunity. OPV contains live, weakened poliovirus. The virus is too weak to cause polio but is strong enough to stimulate an immune response. OPV was the recommended vaccine since its introduction until 2000, when IPV became the preferred vaccine because of rare side effects associated with OPV.
  
  

Vaccine Risks

• OPV, because it contains a live virus, may cause polio in the vaccine recipient. Vaccine-associated paralytic poliomyelitis (VAPP) occurred in approximately 1 in 2.4 million OPV doses when OPV was the preferred vaccine, according to the CDC. VAPP is believed to be caused by mutations of the weakened virus that result in a more active form. Poliovirus resides in the intestine and is shed in the feces, which is how the disease spreads from person to person. The live virus in OPV, although weakened, is also shed in feces up to six weeks after each dose. Therefore, it is possible for caretakers of recently vaccinated infants to contract polio while changing diapers if the caretaker has a weakened immune system. IPV cannot cause VAPP because it does not contain live virus. The most common side effects with IPV are soreness at the injection site, fever, swelling, fussiness and drowsiness, according to Sanofi Pasteur, manufacturer of the IPV available in the U.S. Allergic reactions may also occur, although these are rare.
  
  

Vaccine Benefits

• Natural polio is eradicated in the U.S., but cases still occur so immunization remains an important public health concern. OPV was instrumental in controlling the widespread polio outbreaks because the shedding of the live virus helped confer immunity to people who did not receive the vaccine. Now that polio is rare, the risk of VAPP outweighs the benefits of OPV. OPV is the preferred vaccine in countries where polio remains common because it stimulates a strong immune response more quickly than IPV. In the U.S., IPV is recommended for all children, but OPV may be preferred in specific situations. For example, children who have not been immunized and who are traveling within four weeks to a country where polio is common or for children whose parents decline the injections required for IPV.
  
  

Current Recommendations

• In the U.S., IPV is administered to children in four doses: at 2 months, 4 months, 6 to 18 months and a booster dose at 4 to 6 years of age.