This study evaluates the immune response and safety of a multicomponent, 2-dose Shigella vaccine in preventing shigellosis in African infants. The candidate vaccine, altSonflex1-2-3, is currently being evaluated in a Phase 2 age de-escalation (from least vulnerable adult population to most vulnerable paediatric population) clinical study in Kenya, with the aim of identifying a preferred dose, using a 3-dose vaccination schedule in infants from 9 months of age (NCT05073003). This Phase 2 clinical study will evaluate the safety and immunogenicity of an alternative 2-dose vaccination schedule.

Inclusion Criteria:

• Participants' parent(s)/ Legally acceptable representative (LAR), who, in the opinion of the investigator, can and will comply with the requirements of the protocol.
• Written or witnessed/thumb printed informed consent obtained from the parent(s)/LAR(s) of the participant prior to performance of any study specific procedure.
• Healthy participants as established by medical history, clinical examination, and laboratory assessment.
• Participants satisfying all screening requirements.
• Participants seronegative for hepatitis B, and hepatitis C.
• A male or female 9 months of age at the time of the first study intervention administration.
• Normal nutritional z-score.
• Previously completed routine childhood vaccinations to the best knowledge of the participant's parent(s)/LAR(s).
• Born at a gestation period of >=37 weeks to the best knowledge of the participant's parent(s)/LAR(s).
• Participants negative for human immunodeficiency virus as confirmed by DNA polymerase chain reaction testing.
• Participants negative for HLA-B27.

Exclusion Criteria:

• Known exposure to Shigella during lifetime of the participant as confirmed during interview with the participant's parent(s)/LAR(s) or documented by participant's records.
• Progressive, unstable, or uncontrolled clinical conditions.
• History (known or suspected) of any reaction or hypersensitivity likely to be exacerbated by any component of the study intervention.
• Major congenital defects, as assessed by the investigator.
• Recurrent history or uncontrolled neurological disorders or seizures.
• Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
• Hypersensitivity (known or suspected), including allergy, to medicinal products, vaccines, or medical equipment whose use is foreseen in this study.
• Clinical conditions representing a contraindication to intramuscular vaccination and blood draws.
• Any behavioral or cognitive impairment or psychiatric disease that, in the opinion of the investigator, may interfere with the participant's ability to participate in the study.
• Acute disease and/or fever (defined as temperature >=38.0°C) at the time of enrollment.
• Any clinically significant hematological and/or biochemical laboratory abnormality.
• Confirmed positive COVID-19 test during the period starting 30 days before the first administration of study interventions (Day -30 to Day 1).
• Any other clinical condition that, in the opinion of the investigator, might pose additional risk to the participant due to participation in the study.
• Acute or chronic clinically significant pulmonary, cardiovascular, hepatic, or renal functional abnormality, as determined by physical examination or laboratory screening tests.
• Use of any investigational or non-registered product (drug, vaccine or invasive medical device) other than the study intervention(s) during the period beginning 30 days before the first dose of study intervention(s) (Day -30 to Day 1), or their planned use during the study period.
• Planned administration/administration of a vaccine/product not foreseen by the Protocol in the period starting 21 days before the first dose and ending after the last dose of study intervention(s) administration with the exception of Coronavirus disease 2019 (COVID-19) vaccines and Expanded Program on Immunization (EPI) vaccines.
• Administration of long-acting immune-modifying drugs at any time during the study period.
• Prior receipt of an experimental Shigella vaccine or live Shigella challenge.
• Prior receipt of a Typhoid conjugate vaccine (TCV).
• Administration of immunoglobulins and/or any blood products or plasma derivatives, or bone marrow transplantation, from birth or planned administration during the study period.
• Chronic administration of immune-modifying drugs (defined as more than 14 days consecutive days in total) and/or planned use of long-acting immune-modifying treatments at any time up to the end of the study.
• Concurrently participating in another clinical study, at any time during the study period, in which the participant has been or will be exposed to an investigational or a non-investigational intervention drug or invasive medical device.
• Any study personnel or immediate dependents, family, or household member.
• Child in care.
• Participants who do not meet eligibility criteria for administration of control vaccines.

Study Sponsor will assess requests from qualified researchers for anonymized individual patient-level data and related study documents. Data sharing is subject to certain criteria, conditions, and exceptions. For further information, refer to https://www.gsk-studyregister.com/About\_GSK\_Patient\_Level\_Data\_Sharing\_Final\_13July2023.pdf

Anonymized IPD will be made available within 6 months of publication of primary, key secondary and safety results for studies in product with approved indication(s) or terminated asset(s) across all indications.

Anonymized IPD is shared with researchers whose proposals are approved by an Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension may be granted, when justified, for up to 6 months.