The main purpose of this study is to evaluate safety and reactogenicity of the investigational pneumococcal vaccine (called Pn-MAPS30plus). PCV20 will be used as a comparator for this study

Inclusion Criteria:

1. Participants' parent(s)/Legally acceptable representative [LAR(s)] who, in the opinion of the investigator, can and will comply with all protocol requirements.
2. Written or witnessed/thumb printed informed consent obtained from the participants' parent(s)/LAR(s) prior to performance of any study-specific procedure.
3. Participant is approximately 2 Months of Age [MOA (42 to 90 days, inclusive)] at time of first study intervention administration.
4. Healthy participants as established by medical history and clinical examination before entering the trial.
5. Participant is a full-term infant (≥37 weeks gestation at birth) with a birth weight of >2.5 kg.

Exclusion Criteria:

1. History of any reaction or hypersensitivity likely to be exacerbated by any component of the study intervention(s).
2. Hypersensitivity to latex.
3. History of microbiologically proven Invasive pneumococcal Disease (IPD).
4. Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
5. Major congenital defects, as assessed by the investigator.
6. Recurrent history or uncontrolled neurological disorders or any neuroinflammatory condition, congenital neurological conditions, encephalopathies, or seizures.
7. Condition that in the judgment of the investigator would make intramuscular injection unsafe.
8. Any other clinical condition that, in the opinion of the investigator, might pose additional risk to the participant due to participation in the study.
9. Use of any investigational or non-registered product (drug, vaccine, or invasive medical device in the country of enrollment) other than the study intervention(s) during the period beginning 30 days before the dose of study intervention(s), or their planned use during the trial period.
10. Previous vaccination with any pneumococcal vaccine.
11. Planned administration/administration of any inactivated or otherwise non live vaccine in the period starting 14 days before and ending 14 days after each dose of study intervention administration or planned administration/administration of any live vaccine in the period starting 28 days before and ending 28 days after each dose of study intervention(s) administration, with the exception of inactivated influenza vaccine which may be administered but must be given at least 7 days before or 15 days after receipt of any study intervention.
12. Receipt of blood or plasma products or immunoglobulins, since birth, or planned receipt during the trial up to 30 days after last study intervention administration.
13. Chronic administration of immune-modifying drugs and/or planned use of long-acting immune-modifying treatments at any time up to the end of the trial since birth. For corticosteroids, this will mean prednisone equivalent ≥0.5 mg/kg/day with maximum of 20 mg/day. Inhaled and topical steroids are allowed.
14. Concurrent participation in another clinical study in which the participant has been or will be exposed to an investigational or non-investigational intervention.
15. Any child of trial personnel or their immediate dependents, family, or household members.
16. Child in care.

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 observer-blind study.