Cross-sectional Study to Assess Persistence of Immunity Conferred by a Single IPV Dose Administered in the Expanded Program on Immunization(EPI) Routine Immunization Schedule

Detailed Summary

In 2015, Strategic Advisory Group of Experts in Immunization (SAGE) recommended the global switch from trivalent to bivalent oral poliovirus vaccine (OPV) that does not contain type 2 poliovirus and introduction of a single dose of inactivated poliovirus vaccine (IPV) to maintain population immunity to type 2 polio to reduce the risk of vaccine derived polio. Following SAGE recommendations, Nepal introduced one dose of IPV in routine immunization in 2015 followed by withdrawal trivalent OPV in April 2016. However, Nepal, like many other countries had to stop vaccination by the end of 2016 because of a global shortage of IPV. Single dose of IPV induces detectable antibodies in 34% to 80% of infants, compared to \>90% after three doses and most of seronegative children (84-98%) are "immunologically primed" by the first dose. Primed individuals produce protective antibody levels in serum within one week of exposure to a new dose of IPV or OPV. However, it is unknown whether seroconversion or priming responses persist, and for how long they persist after the single dose of IPV. IPV immunogenicity for vaccine delivered low-resource countries may also be inferior to that observed in clinical trials because of program factors that decrease vaccine efficacy. This cross sectional study aims to determine whether the immune response provided by a single dose of IPV delivered through routine immunization services persists for more than a year. The study will be implemented in three study sites in Kathmandu, Nepal during November 2018- July 2019. Information generated from this study is expected to allow better estimation of children partially protected (primed) or fully protected against type 2 poliovirus depending on coverage and time since last IPV vaccination. These estimates will help inform the Global Polio Eradication Initiative (GPEI) on vaccine choices for responding to type 2 vaccine derived poliovirus (VDPV) outbreaks and will help guide decisions on polio immunization schedules for Nepal and for other countries in future.

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