The purpose of this study is to learn about the safety of a new pneumococcal vaccine and how the new pneumococcal vaccine helps to fight against germs that can cause pneumonia (lung infections), meningitis (brain infections), and otitis media (ear infections) in infants when compared to the pneumococcal vaccine that is currently in use, 20vPnC (Prevnar 20®).

This study will test if the new pneumococcal vaccine is as safe as the one that is currently in use. It will also assess how the new vaccine works in comparison to the one that is currently in use when given with other childhood vaccines.

To measure how the new pneumococcal vaccine compares to the current one, blood samples will be used to measure the body's ability to create proteins to fight those germs. This new vaccine can possibly provide additional protection against germs that cause pneumococcal disease that are not included in the vaccines that are currently given to infants. Pneumococcal disease includes a variety of infections caused by a specific germ, Streptococcus pneumoniae.

There are three groups in this study. All participants will be assigned to one of the three groups. This study is seeking participants who are:

• infants who are 2 months of age in Group 1;
• infants who are 2 to 6 months of age in Groups 2 and 3; and
• said to be healthy by the study doctor

About 3000 infants will be assigned to Group 1. The infants in this group will have a 1 in 2 chance (50%) of receiving either PG4 (new vaccine) or 20vPnC (currently in use) into the left thigh muscle at 2, 4, 6, and 12 to 15 months of age.

About 140 infants from outside the United States will be assigned to Group 2. The infants in this group will have a 1 in 2 chance (50%) of receiving either PG4 or 20vPnC into the left thigh muscle at 2 to 6, 3 to 8, 4 to 10, and 12 to 15 months of age.

About 90 infants from outside the United States will be assigned to Group 3. The infants in Group 3 will have a 1 in 3 chance (33%) of receiving either PG4 into the left thigh muscle, PG4 under the skin of the left thigh, or 20vPnC into the left thigh muscle at 2 to 6, 3 to 8, 4 to 10, and 12 to 15 months of age.

Infants in Group 1 will take part in this study for about 16 to 19 months (about 1 and a half years). Infants in Groups 2 and 3 will take part in this study for 12 to 21 months (about 1 to 1 and a half years). During this time, infants will have 6 study clinic visits and 1 phone call. At these study clinic visits, parent(s)/legal guardian(s) will be asked if the infant experienced any side effects. A side effect is an unintentional or unexpected reaction to a vaccine. Infants will have 3 blood samples collected.

Inclusion Criteria:

• infants who are 2 months of age in Group 1.
• infants who are 2 to 6 months of age in Groups 2 and 3.
• Healthy infants determined by clinical assessment, including medical history and clinical judgment, to be eligible for the study.

Exclusion Criteria:

• History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis).
• 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 investigational product 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.