This study is about a new pneumococcal vaccine for toddlers, which helps protect against infections like pneumonia. We want to see if the vaccine is safe and how it affects the immune system. Kids will be part of the study for about 6 or 8 months, depending on their group. There are two groups: one gets 1 dose and has 2 clinic visits and 1 phone call; the other gets 2 doses and has 3 clinic visits and 1 phone call. During clinic visits, we will check for side effects and take blood samples.

• Study Length: 6 or 8 months, depending on group.
• Visits: 2 or 3 clinic visits and 1 phone call, based on the group.
• Eligibility: Healthy toddlers, aged 12-15 months, who already had 3 doses of 20vPnC.

If your child has had a bad reaction to a vaccine before or has certain health issues, they might not be able to join. It's important they haven't had any other pneumococcal vaccine except 20vPnC. Please consider these points before deciding to participate.