A Study to Learn About How a New Pneumococcal Vaccine Works in Adults

The purpose of this study is to learn about the safety and tolerability of a pneumococcal vaccine in adults. Participants will receive either: * an experimental PG4 vaccine * a PG4 vaccine comparator * a standard 20vPnC vaccine comparator * placebo. A placebo does not have any medicine in it but looks just like the study medicine. Participants will take part in this study for up to 18 months depending on which group they are assigned to. During this time, the participants will receive up to two doses of study vaccine or comparator and take part in follow-up visits. At these clinic visits, participants will be asked if any side effects were experienced. The participants will also have to give blood samples during clinic visits.

NCT Number	NCT07086677
Lead Sponsor	Pfizer
Conditions	Streptococcus Pneumoniae
Enrollment	380 participants
Start Date	2025-07-22
Primary Completion	2027-10-21 (estimated)
Study Completion	2027-10-21 (estimated)
Updated on ClinicalTrials.gov	2026-06-22