This is a randomized, double-blind, placebo-controlled, multicenter, 2-arm (1:1), parallel group, efficacy, and safety/tolerability fixed-dose study of SPN-812 in preschool-age children (4 to 5 years old) with a DSM-IV-TR diagnosis of ADHD. Approximately 286 subjects will be randomized to either SPN-812 or matching placebo in a 1:1 ratio (143 subjects per arm). Following up to 4 weeks of screening, subjects will be treated with study medication (SM) for 6 weeks, then will either be enrolled in a separate OLE study or followed for an additional 1 week for safety. The total duration of the study is up to 10 weeks.

A germ called Streptococcus pneumoniae (also known as S pneumoniae) is a leading cause of serious diseases including infection of the lungs (pneumonia), infection of the brain lining (meningitis), infection of the blood (bacteremia) and infection of the ears (otitis). There are more than 90 different types of S pneumoniae, some of which cause more serious infections than others. 20-valent (meaning the vaccine protects against 20 different types of S. pneumoniae) pneumococcal conjugate vaccine (Prevnar 20®; 20vPnC) was approved in 2021 first in adults then in children in the United States in 2023, to prevent pneumococcal disease.

The study vaccine, 25-valent pneumococcal conjugate vaccine (25vPnC, PG4 vaccine, pneumococcal fourth-generation vaccine) contains the same components found in 20vPnC, one of which has been changed, but with 5 additional components to help expand protection against 25 types of S pneumoniae. The study vaccine is not approved by the United States Food and Drug Administration (FDA) or elsewhere around the world.

This study will look at how a new pneumococcal vaccine will work in healthy infants while expanding protection against pneumococcal disease due to the germ called S pneumoniae; and, how the new study pneumococcal vaccine will work together with recommended childhood shots.

This study will last for about 16 to 19 months and will have at least 6 visits and 1 telephone contact, about 6 months after your child's last study vaccination.