vaccine, administered orally and in three or more spread doses in order to generate adequate levels of seroconversion [ IATE:1431879 ], that consists of a mixture of live attenuated poliovirus strains [ IATE:1141473 ] of each of the three serotypes [ IATE:1542840 ], selected by their ability to mimic the immune response following infection with wild polioviruses, but with a significantly reduced incidence [ IATE:1569465 ] of spreading to the central nervous system