Safety and Immunogenicity of 20vPnC in Toddlers With 2 Prior Doses of Prevenar 13

The purpose of this study is to understand the safety and effects of a study vaccine (20vPnC) in toddlers who had 2 prior doses of Prevnar 13. This study is being conducted in children who: * are between 12 to 23 months of age; * are healthy as determined by the study doctors; * have received 2 doses of Prevnar 13 during the first year in life. Participants in this study will receive either 1 dose or 2 doses of the study vaccine or 1 dose of Prevnar 13 as a shot in the muscle. During the study, participants will have to come to the study clinic to receive the vaccines and have blood sample collected. The study team will work with participants\' parents or legal guardians to monitor any unwanted reactions to the vaccines. Participants are expected to take part in this study for about 1 or 3 months, for 1 dose or 2 dose schedules, respectively.