COVID-19 is evolving right under our very noses. It’s transforming from a pandemic disease to an endemic one — a disease that lives in the area, meaning a constant risk. Endemic diseases can be mild, like the common cold, but they can also be deadly. Malaria, yellow fever, diphtheria, smallpox, and other diseases are or have been endemic in other times and places. As COVID-19 becomes endemic, uncertainty is likely to increase, at least for a while, about the effects and severity of the disease, how exactly it spreads, and what it means to live with it on a daily basis. But as Philadelphia’s battle with tuberculosis more than a century ago shows, even without perfect information, health and other leaders can still make just decisions.