Three doses of live-attenuated OPV produce protective antibodies to all three poliovirus types in more than 95% of recipients. OPV produces excellent immunity in the intestine, the primary site of wild poliovirus entry, which helps prevent infection with wild virus in areas where the virus is endemic. The live virus used in the vaccine can rarely shed in the stool and can rarely spread to others within a community. The live virus also has stringent requirements for transport and storage, which are a problem in some hot or remote areas. As with other live-virus vaccines, immunity initiated by OPV is probably lifelong.The trivalent (against wild types 1, 2, and 3) OPV has been used to nearly eradicate polio infection worldwide. Led by the Global Polio Eradication Initiative, 155 countries switched to use the bivalent (against wild types 1 and 3) between 17 April and 1 May 2016. The bivalent OPV is more effective against types 1 and 3, but does not cover type 2. The United States as of 2017 continues to recommend the use of a trivalent version, but a fully inactivated version. The switch to the bivalent vaccine and associated missing immunity against type 2 strains, among other factors, led to outbreaks of circulating vaccine-derived poliovirus type 2(cVDPV2), which increased from 2 cases in 2016 to 1037 cases in 2020.
As a response, a novel oral polio vaccine type 2 (nOPV2) was developed with the aim to provide a safer form of vaccination against type 2 strains with less risk of reverting to infectious polio. Schedule
In countries with endemic polio or where the risk of imported cases is high, the WHO recommends OPV vaccine at birth followed by a primary series of three OPV doses and at least one IPV dose starting at 6 weeks of age, with a minimum of 4 weeks between OPV doses. In countries with >90% immunization coverage and low risk of importation, the WHO recommends one or two IPV doses starting at 2 months of age followed by at least two OPV doses, with the doses separated by 4–8 weeks depending on the risk of exposure. In countries with the highest levels of coverage and the lowest risks of importation and transmission, the WHO recommends a primary series of three IPV injections, with a booster dose after an interval of six months or more if the first dose was administered before 2 months of age. Side effects
The inactivated polio vaccines are very safe. Mild redness or pain may occur at the site of injection. Oral polio vaccine results in vaccine-associated paralytic poliomyelitis in about three per million doses. They are generally safe to give to those who are pregnant, and those who have HIV/AIDS, but who are otherwise well.