A Phase 4 study to evaluate the safety and immunogenicity of monovalent oral polio vaccine type 2 in healthy IPV-vaccinated children aged 1 to 5 years in Lithuania.

Sabin 2 will be withdrawn from routine use globally from April 2016 as per the SAGE recommendations at the time of writing this protocol. After this cessation of OPV2, stockpiles of mOPV2 will be maintained for potential use if necessary in response to a future outbreak. However, there is a risk of cVDPV2 from Sabin 2 in settings of low population immunity. Research is ongoing to develop vaccines that are genetically more stable than the currently available Sabin 2-containing OPVs. To generate data on immunogenicity, safety, and genetic stability on the Sabin 2 vaccine (mOPV2) and as a future comparator for new polio vaccine research after the global switch from tOPV to bOPV, this study with mOPV2 is performed to evaluate safety, immunogenicity (humoral and intestinal) and genetic stability endpoints of mOPV2 in children aged 1 to 5 years for better understanding of the stockpile use of this vaccine, and any potential new polio vaccine with a type 2 component in the future.

Inclusion Criteria:

1. 1 to 5 years of age, previously vaccinated with three or four doses of IPV.
2. Healthy without obvious medical conditions that preclude entry of the subject into the study as established by the medical history and physical examination.
3. Written informed consent obtained from 1 or 2 parent(s) or legal guardian(s) as per country regulations.

Exclusion Criteria:

1. Previous vaccination against poliovirus outside the national immunization schedule.
2. Any confirmed or suspected immunosuppressive or known immunodeficient condition including human immunodeficiency virus (HIV) infection.
3. Family history of congenital or hereditary immunodeficiency.
4. Major congenital defects or serious uncontrolled chronic illness (neurologic, pulmonary, gastrointestinal, hepatic, renal, or endocrine).
5. Known allergy to any component of the study vaccines or to any antibiotics.
6. Administration of immunoglobulins and/or any blood products since birth or planned administration during the study period.
7. Acute severe febrile illness at day of vaccination deemed by the Investigator to be a contraindication for vaccination (the child can be included at a later time if within age window and all in/exclusion criteria are met.).
8. Member of the subject's household (living in the same house or apartment unit) has received OPV in the last 3 months.
9. Subject who, in the opinion of the Investigator, is unlikely to comply with the protocol or is inappropriate to be included in the study for the safety or the benefit-risk ratio of the subject.

3 months