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.

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 asset(s) with development terminated 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.

This is an open-label study.