Study of a Novel Type 1 Oral Poliomyelitis Vaccine in Bangladesh

Frequency of serious adverse events (SAEs) from the time of first study vaccination through the end of the study

Serious adverse event is any adverse event that results in any of the following outcomes: 1. Death 2. Is life-threatening (life-threatening means that the study participant was, in the opinion of the site PI or PATH, at risk of death at the time of the event; it does not refer to an event which hypothetically might have caused death if it were more severe). 3. Requires inpatient hospitalization or prolongation of existing hospitalization 4. Results in persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions 5. Important medical event that may not result in one of the above outcomes but may jeopardize the health of the study participant and require medical or surgical intervention to prevent one of the outcomes listed in the above definition of serious adverse event

Frequency of solicited adverse events (AEs) for 7 days (day of vaccination and 6 following days) after each vaccination

Solicited AEs are pre-specific AEs that are common or known to be associated with vaccination that are actively monitored as potential indicators of vaccine reactogenicity. The following specific solicited AEs will be monitored for this trial: * Fever (axillary temperature ≥ 37.5°C) * Vomiting * Diarrhea * Irritability * Decreased feeding or appetite * Fatigue or decreased activity

Frequency of unsolicited AEs for 28 days (day of vaccination and 27 following days) after each vaccination

Unsolicited AEs are any AEs reported spontaneously by the participant's parent, observed by the study personnel during study visits or identified during review of medical records or source documents. In the absence of a diagnosis, abnormal physical examination findings or abnormal clinical safety laboratory test results that are assessed by the investigator to be clinically significant will be reported as an AE.

Post-vaccination frequency of seroconversion of type 1 anti-polio serum neutralizing antibody (NAb).

Following two doses of nOPV1, at dose levels of 10\^6.5 and 10\^7.0 CCID50/dose, compared to mOPV1, in healthy neonates. For unvaccinated neonates, seroconversion will be defined as either a minimum 4-fold higher antibody titer relative to the expected level of maternal antibody and seropositivity (reciprocal titer ≥ 8) at the post-vaccination time point among those initially seropositive, or post-vaccination seropositivity among those initially seronegative.

Post-vaccination frequency of seroconversion of type 1 anti-polio serum NAb.

To assess the seroconversion rate elicited by nOPV1 at dose levels of 10\^6.5, 10\^7.0 and 10\^7.5 CCID50/dose following one and three doses in healthy neonates compared to mOPV1. To assess the seroconversion rate elicited by nOPV1 at dose levels of 10\^5.5, 10\^6.0 and 10\^6.5 CCID50/dose following one or two doses in healthy young children compared to mOPV1. To assess the seroconversion rate elicited by nOPV1 at dose levels of 10\^5.5 and 10\^6.0 CCID50/dose following one or two doses in healthy infants compared to mOPV1.

Median type 1 anti-polio serum NAb titers.

Elicited by nOPV1, compared to that of mOPV1, following one or two doses in healthy young children, and one, two or three doses in infants and neonates.

Type 1 anti-polio serum NAb Geometric Mean Titer (GMT).

Elicited by nOPV1, compared to that of mOPV1, following one or two doses in healthy young children, and one, two or three doses in infants and neonates.

Post-vaccination GMT ratios of type 1 anti-polio serum NAb, adjusted for baseline immunity.

Elicited by nOPV1, compared to that of mOPV1, following one or two doses in healthy young children, and one, two or three doses in infants and neonates.