The Invisible Shield, a four-part documentary series from RadicalMedia made possible by Bloomberg Philanthropies, reveals how the field of public health has saved countless lives in the U.S., protecting people from the constant threat of disease and increasing lifespans. The series explores the hidden public health infrastructure that makes modern life possible. It highlights the thousands of unsung heroes — physicians, nurses, scientists, activists, reformers, engineers, and government officials — who work together to improve health outcomes, from the days of cholera and smallpox through the most recent battle with COVID-19.The Invisible Shield on PBS, with all four episodes available for streaming on PBS.org and the PBS App.