A Study to Learn About the Safety of an Expanded Pneumococcal Vaccine in Healthy Infants

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

\- infants who are about 2 months of age

About 2400 infants will be assigned by chance to one of the two groups to receive 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.

Infants will take part in this study for about 16 to 19 months (about 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.