A Study to Evaluate the Safety and Immunogenicity of VLP-Polio in Infants and Toddlers

Inclusion Criteria: * Healthy toddlers aged 12-18 months at the time of screening, and have completed primary immunization of polio vaccine according to the national government program in the first year of life. * Healthy infants aged 6 weeks to 2 months (42 to 98 days, with the day of birth considered day of life 1), and who have not received any polio vaccines. * Able to obtain written informed consent from parent(s) or legal guardian(s). * Participants and their parents or legal guardian(s) can comply with trial procedures, are available for the duration of follow-up, and have a suitable telephone contact available. Exclusion Criteria: Exclusion criteria for the first dose: * Current polio disease or history of polio disease. * Toddlers who have an interval of less than 5 months since their last dose of the polio vaccine. * Infants born at \< 37 weeks of gestation. * Children with a birth weight \< 2500g and a body weight \< 3500g at the time of enrollment. * Body temperature ≥37.5°C (the visit may be rescheduled when this criterion is met). * Have congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc. * Any moderate or severe acute illness. * Any abnormal vital signs. * History of epilepsy, convulsions, or parent with congenital cognitive disability, dementia, or intellectual disabilities. * Have received immunosuppressive treatment, cytotoxic treatment, glucocorticoid treatment, etc. (excluding local treatment, surface treatme…