The purpose of this study is to understand the safety and effects of a study vaccine (20vPnC) in infants and toddlers.

This study is enrolling participants who are:

• Born after at least 36 weeks of pregnancy and about 2 months of age at the time of entering the study
• Have a bodyweight of at least 3 kg

Participants will receive either the study vaccine (20vPnC) or a licensed vaccine (13vPnC) as a 4-dose schedule as a shot in the muscle. Participants will receive Dose 1 on study day 1. Dose 2 will be given 28-70 days after Dose 1, and Dose 3 will be given 28-70 days after Dose 2. Dose 4 will be given at 365-455 days (approximately 12-15 months) of age.

Participation in the study will take approximately 15 months, during which participants will come to the study clinic for 6 times. The study team will ask questions about the participant's health and take some blood samples during the visit.

Inclusion Criteria:

• Male or female infants born at ≥36 weeks of gestation and approximately 2 months of age at the time of consent
• Healthy infants determined by clinical assessment, including medical history and clinical judgment, to be eligible for the study
• Weight of 3.0 kg or greater at the time of randomization

Exclusion Criteria:

• History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of 13vPnC, 20vPnC, or any other diphtheria toxoid-containing vaccine.
• Major known congenital malformation or serious chronic disorder
• Other acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or study intervention administration or may interfere with the interpretation of study results and, in the judgment of the investigator, would make the participant inappropriate for entry into this study
• Previous vaccination with any licensed or investigational pneumococcal vaccine, or planned receipt through study participation.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.