This study is looking for healthy children and adolescents, ages 2 to 17 years old that are interested in getting a pneumonia vaccine. Most children get a pneumonia vaccine in the first year of life. This research study will be testing a new version of the pneumonia vaccine that is designed to protect your child against additional strains of pneumonia. This means your child will receive one dose of the updated version of the vaccine, PCV21, or your child will receive PCV20, the currently administered pneumonia vaccine in the U.S. You will be expected to accompany your child for 2 clinic visits that will include your child’s vaccine injection and 2 blood draws. You must complete two telephone visits as well. The study duration is 6 months. Your child may qualify for enrollment if they are healthy and are ages 7 months to 23 months, but have never had a pneumonia vaccine. Compensation will be provided. If you are interested in enrollment or need more information, please contact Alexis, Misty, or Sama at 205-638-2629. Email as well at mlpurser@uabmc.edu