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

Ali F. Saleem, Ondrej MacH, Mohammad T. Yousafzai, Asia Khan, William C. Weldon, M. Steven Oberste, Syed S. Zaidi, Muhammad M. Alam, Farheen Quadri, Roland W. Sutter, Anita K.M. Zaidi

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23 Citations (Scopus)


Background. We assessed immunity against polioviruses induced with a new Pakistani poliovirus immunization schedule and compared it to alternative poliovirus immunization schedules. Methods. Newborns were randomized to undergo vaccination based on 1 of 5 vaccination schedules, with doses administered at birth and at 6, 10, and 14 weeks of age. Arm A received inactivated poliovirus vaccine (IPV) at all time points. Arm B received bivalent oral poliovirus vaccine (bOPV) at all time points. Arms C and D received bOPV at the first 3 time points and bOPV plus IPV at the final time point (the current schedule). Arm E received trivalent OPV (tOPV) at all time points. At 22 weeks of age, all children received 1 challenge dose of tOPV, and children in arm D received 1 additional IPV dose. Sera were analyzed for the presence of poliovirus neutralizing antibodies at birth and 14 and 22 weeks of age. Results. Seroconversion for poliovirus type 1 (PV1) at 22 weeks of age was observed in 80% of individuals in arm A, 97% in arm B, 94% in arm C, 96% in arm D, and 94% in arm E; for PV2, seroconversion frequencies were 84%, 19%, 53%, 49%, and 93%, respectively; and for PV3, seroconversion frequencies were 93%, 94%, 98%, 94%, and 85%, respectively. Conclusions. The 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.

Original languageEnglish
Pages (from-to)443-450
Number of pages8
JournalJournal of Infectious Diseases
Issue number3
Publication statusPublished - 17 Jan 2018


  • Polio immunity
  • immunization
  • outbreak
  • poliovirus 2


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