Why can a monovalent oral polio vaccine be more effective against one serotype than a trivalent vaccine?

A monovalent oral polio vaccine (mOPV) is more effective against a specific serotype than a trivalent vaccine (tOPV) because of its increased specificity. By containing only one of the three live attenuated poliovirus serotypes, the mOPV focuses the immune response on that single target without the potential for interference between different viral strains present in a trivalent preparation.

For example, a single dose of mOPV1 confers immunity to serotype 1 in approximately 70 to 80 percent of children, whereas a single dose of tOPV—which targets all three serotypes (PV1, PV2, and PV3)—confers immunity to serotype 1 in only about 20 to 40 percent of children. This enhanced efficacy makes monovalent oral poliovirus vaccines a valuable tool in specific immunization strategies, particularly in regions where a particular serotype remains a significant threat.12