This study involves comparing an investigational (study) vaccine against a placebo (injection with no active ingredient) to see if the vaccine can prevent COVID-19. The vaccine is given by injection. Adults 18-85 years old who are not pregnant, in good general health, and have not been previously diagnosed with COVID-19 can participate in the study. The study doctor will also assess whether you are at risk of COVID-19 infection before you can participate. Things the study doctor may consider include the type of work you do, your lifestyle, and any medical conditions you may have.