Immunogenicity of Different Routine Poliovirus Vaccination Schedules: a Randomized Controlled Trial, Karachi, Pakistan

Document Type



Paediatrics and Child Health


Background: We assessed immunity against polioviruses induced with new Pakistani immunization schedule and compared it with alternative immunization schedules.Methods: Newborns were randomized to receive one of the following vaccination schedules, administered at birth, 6, 10, and 14 weeks of age. Arm A: 4x IPV; Arm B: 4x bOPV; Arm C and D: bOPV, bOPV, bOPV, bOPV+ inactivated poliovirus vaccine (IPV); Arm E: 4x trivalent oral poliovirus vaccine (tOPV). At 22 weeks of age, children received one challenge dose of tOPV, and children in arm D received one additional IPV dose. Sera were analyzed for presence of polio neutralizing antibodies at birth, 14, and 22 weeks of age.Results: Study arms A-E, the seroconversion for PV1 at 22 weeks of age was 80%, 97%, 94%, 96%, 94% respectively; for PV2: 84%, 19%, 53%, 49%, 93%; and for PV3: 93%, 94%, 98%, 94%, 85%.Interpretation: Current immunization schedule in Pakistan induced high seroconversion rates for PV1 and PV3; however, it induced PV2 seroconversion in only half of study subjects. There is a growing cohort of young children in Pakistan who are unprotected against PV2; and this creates an increasing risk of a large-scale outbreak of poliomyelitis caused by circulating vaccine-derived PV2.


The Journal of Infectious Diseases