The oral polio vaccine (OPV) was developed in 1961 by Albert Sabin. Also called “trivalent oral polio vaccine” or “Sabin vaccine”, OPV consists of a mixture of live, attenuated (weakened) poliovirus strains of all three poliovirus types.
OPV produces antibodies in the blood to all three types of poliovirus. In the event of infection, these antibodies protect against paralysis by preventing the spread of wild poliovirus to the nervous system. OPV also produces a local, mucosal immune response in the mucous membrane of the intestines. In the event of infection, these mucosal antibodies limit the replication of the wild poliovirus inside the intestine. This intestinal immune response to OPV is thought to be the main reason why mass campaigns with OPV can rapidly stop person-to-person transmission of wild poliovirus.
Although OPV is safe and effective, in extremely rare cases (approx. 1 in every 2.7 million first doses of the vaccine) the live attenuated vaccine virus in OPV can cause paralysis. In some cases it is believed that this vaccine-associated paralytic polio (VAPP) may be triggered by immune deficiency. The extremely low risk of VAPP is well known and accepted by most public health programmes in the world because without OPV, hundreds of thousands of children would be crippled every year. A second disadvantage is that very rarely the virus in the vaccine may genetically change and start to circulate among a population. These viruses are known as circulating vaccine-derived polioviruses (cVDPV).
OPV is an extremely safe vaccine. All OPV used in supplementary immunization activities for the Global Polio Eradication Initiative is pre-qualified by WHO and procured through UNICEF. In 2006, WHO issued a statement to affirm the quality and safety of OPV.
OPV is highly effective against all three types of wild poliovirus. When this vaccine is used however, there is competition among the three viruses to cause immunity, which results in protection but not with equal efficiency for each type: it is most effective against type 2.One dose of OPV produces immunity to all three poliovirus serotypes in approximately 50% of recipients. Three doses produce immunity in more than 95% of recipients. Immunity is long-lasting and probably life-long.
In most countries, OPV remains the vaccine of choice in routine immunization schedules and supplementary immunization activities. Where more than one type of wild poliovirus is circulating, OPV is epidemiologically and operationally the best vaccine to use because protection develops to each of the three types of polio virus.
WHO position statement: safety and pre-qualification of oral polio vaccine (OPV)
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