Duration of IPV Priming and Antibody Decay

This is an open-label randomized phase IV clinical trial assessing immunogenicity of poliovirus vaccines.Participants will be enrolled at 6 weeks of age and followed to 18 months of age. The study will recruit 1645 participants in five arms.

Poliomyelitis is an acute infection caused by polioviruses. Oral poliovirus vaccines are live attenuated viral vaccines and the vaccine virus in OPV can mutate and acquire neurovirulence causing paralysis either due to vaccine-associated paralytic polio (VAPP) or due to circulating vaccine-derived polioviruses (cVDPV), in which the attenuated vaccine virus not only acquires the ability to cause paralysis but can also circulate similar to wild poliovirus (WPV). Therefore, polio eradication will require eventual cessation of all OPVs.

Wild poliovirus type 2 (WPV2) was declared eradicated in September 2015. Since then paralysis associated with type 2 poliovirus has continued mainly due to vaccine derived polio viruses (VDPVs) from type 2 OPV (OPV2). Due to the continued threat of paralysis from a mutated, neurovirulent and vaccine-derived type 2 poliovirus, the Strategic Advisory Group of Experts on Immunization (SAGE), a global advisory committee on immunization, recommended a phased cessation of OPV starting with OPV2. By May 2016, OPV2 was successfully withdrawn globally when trivalent OPV (tOPV) was replaced with bivalent OPV (bOPV), which was preceded by a phased introduction of inactivated poliovirus vaccine (IPV). SAGE has recommended at least one dose of IPV at age ≥14 weeks because IPV immunogenicity is expected to be highest after maternal antibodies have declined by age 14 weeks. However, studies have not assessed if priming after one IPV dose declines over time.

Types 1 and 3 OPV cessation is likely expected in 2020-2022, i.e. 1-2 years after certification of global interruption of wild poliovirus transmission. After cessation of bOPV, IPV will be used for routine polio vaccination for 5-10 years.Recently, SAGE recommended that IPV be used after global OPV withdrawal with an IPV schedule that achieves at least 90% seroconversion with two full or fractional doses. SAGE has recommended that the first dose be administered after 14 weeks of age and an interval of at least 4 months between two IPV doses. In the proposed clinical trial, immunogenicity of two IPV doses with schedules that are likely to achieve 90% immune response to all poliovirus types is being assessed to inform SAGE policy deliberations on potential IPV schedules after OPV cessation. A head-to-head comparison of different IPV schedules is important to determine the immunogenicity of the schedules under similar conditions and evaluate the differences in population immunity, a product of immunogenicity and vaccination coverage, with the different IPV schedules.

Eligibility Criteria:
Inclusion Criteria:

* Healthy infants 6 weeks of age (range: 42-48 days).
* Parents that consent for participation in the full length of the study.
* Parents that are able to understand and comply with planned study procedures.

Exclusion Criteria:

* Parents and infants who are unable to participate in the full length of the study.
* A diagnosis or suspicion of immunodeficiency disorder either in the infant or in an immediate family member.
* A diagnosis or suspicion of bleeding disorder that would contraindicate parenteral administration of IPV or collection of blood by venipuncture.
* Acute diarrhoea, infection or illness at the time of enrollment (6 weeks of age) that would require infant's admission to a hospital.
* Acute vomiting and intolerance to liquids within 24 hours before the enrollment visit (6 weeks of age).
* Evidence of a chronic medical condition identified by a study medical officer during physical exam.
* Receipt of any polio vaccine (OPV or IPV) before enrollment based upon documentation or parental recall.
* Known allergy/sensitivity or reaction to polio vaccine, or its contents.
* Infants from multiple births. Infants from multiple births will be excluded because the infant(s) who is/are not enrolled would likely receive OPV through routine immunization and transmit vaccine poliovirus to the enrolled infant.
* Infants from premature births (\<37 weeks of gestation).