Comparing immune response to oral polio vaccine administered at short intervals with vaccine administered at standard intervals in healthy newborns in Pakistan

INTERVENTION: Three intervention arms: 1) Birth tOPV; day 42 mOPV1, day 49 mOPV1, day 79 tOPV, day 107 tOPV 2) Birth tOPV; day 42 mOPV1, day 56 mOPV1, day 86 tOPV, day 114 tOPV 3) Birth tOPV; day 42 mOPV1, day 72 mOPV1, day 102 tOPV, day 130 tOPV tOPV: trivalent oral polio vaccine; mOPV1: monovalent type 1 oral polio vaccine Dose for all oral polio vaccines: two drops CONDITION: poliomyelitis PRIMARY OUTCOME: A schedule of two doses of mOPV1 administered at a 7 or 14 day interval following a previous mOPV1 dose administered at 42 days induces comparable levels of seroconversion against poliovirus type 1 compared to a schedule of two doses of mOPV1 given at a standard interval of 30 days apart SECONDARY OUTCOME: A schedule of two doses of mOPV1 administered at a 7 or 14 day interval following a previous mOPV1 dose administered at 42 days induces comparable levels of seroconversion against poliovirus type 1 compared to a schedule of two doses of bOPV1&3 administered at a standard interval of 30 days apart. INCLUSION CRITERIA: Infants born healthy (> 2.5 kg birth weight, immediate cry, no neonatal IMCI danger signs) at the study sites (home or health facility births assisted by study‐Trained Birth Attendants/other health personnel) and not planning to travel away during entire the study period (birth‐102 days).