Monovalent oral polio vaccines (mOPV) consist of live, attenuated (weakened) poliovirus strains of either type 1 (mOPV1) or type 3 (mOPV3) poliovirus only. Unlike OPV, it does not contain the other two types of poliovirus. The vaccine gives protection against one type of poliovirus only (either type 1 or type 3 depending on the vaccine).
Monovalent oral polio vaccines were used extensively in the early days of polio vaccination in the late 1950s and early 1960s. However, from 1963, mOPVs were replaced by OPV, where protection against all three types of wild poliovirus could be given at the same time – an important consideration when more than one type of wild poliovirus was circulating.In 2005, new mOPVs were introduced to more rapidly interrupt the final strains of poliovirus transmission around the world. Monovalent oral polio vaccine type 1 was first used in India in April 2005, and has subsequently been used in many areas since the adoption of a strategy to primarily target type 1 poliovirus, the type which is the more paralytic and spreads more easily than type 3.Monovalent oral polio vaccine type 3 was introduced in India and Afghanistan in 2005 to interrupt endemic strains of polio type 3 in targeted areas. Experience in western Uttar Pradesh and in parts of Bihar demonstrated that rapid, large-scale mOPV3 campaigns had a significant impact on type 3 transmission. The vaccine has subsequently been used in Nigeria and Pakistan and to tackle an outbreak of imported poliovirus in Chad.
Based both on years of use and the administration of tens of millions of doses, monovalent oral polio vaccines are known to be a safe, with safety records similar to trivalent OPV.
Approximately twice as many children develop immunity to poliovirus type 1 after the first dose of mOPV1 compared with the first dose of OPV. With three doses of mOPV1, over 90% of children will develop immunity; the same of tOPV will confer immunity on only 70–75% of children.Approximately 70% of children develop immunity to poliovirus type 3 after the first dose of mOPV3 compared with approximately 30% of children after the first dose of OPV.
The implications for the remaining polio-endemic states of India are to vaccinate all children multiple times with mOPV1 and sustain these levels until transmission has been successfully interrupted.
1Grassly NC et al, Protective efficacy of a monovalent oral type 1 poliovirus vaccine: a case-control study, The Lancet, 12 April 2007.
Monovalent oral polio vaccines are recommended for use in supplementary immunization campaigns in areas where only wild poliovirus type 1 or type 3 alone is circulating. It is not recommended as a substitute for OPV in routine immunization programmes.Two doses of mOPV administered within two weeks forms the basis of the new Short Interval Additional Dose (SIAD) approach, which is intended to rapidly boost population immunity in Asia.
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