The main purpose of the study is to assess safety when both vaccines are administered together with a six-month follow-up. The trial includes 600 adults who will have received their second dose of Pfizer's COVID-19 vaccine at least six months before the coadministration study.

Participants will be randomized into three groups:

• Pneumococcal vaccine plus COVID-19 vaccine booster
• Pneumococcal plus a placebo
• COVID-19 vaccine booster and a placebo

The Pfizer-BioNTech COVID-19 vaccine is based on messenger RNA (mRNA) technology and has been shipped to 91 countries and territories around the world as part of an emergency use authorization (EUA) from the U.S. Food and Drug Administration (FDA).

The company's pneumococcal vaccine was accepted for priority review for a biologics license application by the FDA in December 2020 and marketing authorization application review by the European Medicines Agency in February 2021. The vaccine includes capsular polysaccharide conjugates for 20 serotypes that are responsible for a majority of currently circulating pneumococcal disease globally.