Every year in the United States, 2 million people become infected with Staphylococcus aureus bacteria—“staph”—and 100,000 of those people die. Skin infections are most common, but staph infections of the lung (pneumonia) and bloodstream (bacteremia) are the deadliest. A vaccine would save lives and money, reduce the use of antibiotics, and slow the spread of antibiotic resistance. That is, if a vaccine is targeted to people when their risk of becoming infected with staph is highest—when they go to the hospital for surgery or some other invasive procedure. That’s because the science suggests that even the most successful vaccine is going to provide immunity for just a limited time.