Long-Term Immunogenicity of the altSonflex1-2-3 Shigella Vaccine in African Children

The current study is a follow-up to 2 previous parent studies, a dose-selection study with 3 different dose-levels of the altSonflex1-2-3 vaccine in a schedule of 3 vaccinations (H06\_01TP study \[NCT05073003, 212149\]) and a study with an alternate 2 vaccination schedule H06\_02TP study \[NCT06663436, 219449\]). The current study aims to assess the longevity of the immune response to the selected dose of the altSonflex1-2-3 vaccine 1, 2, and 3 years after the last vaccination in African children. The study involves no new vaccinations but will collect immunogenicity blood samples from participants.

Inclusion Criteria: * Children who, as infants, previously participated in two completed studies (H06\_01TP or H06\_02TP) and were vaccinated with 3 or 2 doses of altSonflex1-2-3 or control vaccines, respectively, completed all previous vaccinations and are 12±1 months after the last altSonflex1-2-3 vaccination. * Individuals in good health as determined by medical history since last study visit and clinical judgment of the investigator. Exclusion Criteria: * Serious and significant progressive, unstable, or uncontrolled clinical condition(s). * Any confirmed or suspected immunosuppressive or immunodeficient condition. * Clinical condition(s) representing a contraindication to blood draws. * Any behavioural or cognitive impairment or psychiatric disease. * Acute disease and/or fever at the time of enrollment. * Individuals with known or suspected HIV infection or HIV-related disease, with history of an autoimmune disorder or any other known or suspected impairment/alteration of the immune system, or under immunosuppressive therapy. * Receipt of immunoglobulins and/or any blood products or plasma derivatives, during the period starting 3 months before each study visit.