A Study to Learn About a COVID-19 Vaccine in Healthy Adults 18 Through 64 Years of Age

The purpose of this study is to learn about the safety and effects of an updated COVID-19 vaccine (called BNT162b2) in adults 18 to 64 years of age. This study is seeking participants who: * are medically stable * have not had a recent COVID-19 infection * have not had a recent vaccination * do not have medical conditions that increase their risk of complications from COVID-19 All participants in this study will randomly receive 1 injection into their arm of either: * BNT162b2 vaccine which targets COVID-19 and is selected for the 2026-2027 COVID-19 season, or * Tdap vaccine which targets tetanus, diphtheria, and pertussis (whooping cough). The study team and participants will not know which injection they receive. We will evaluate safety and SARS-CoV-2 spike protein levels in people receiving each of these vaccines. Participants will be in the study for about 12 months.