Herd Immunity What Is it?

A term traditionally used in vaccination, herd immunity through has been used by some leaders across the world as a way but which to return to normality. We discuss what this means and how it is reached. Dr. Ali Mokdad, a senior faculty member of the Institute for Health Metrics and Evaluation and a former top official at the CDC and Thomas J. Bollyky, director of the global health program and senior fellow for global health, economics, and development at the Council on Foreign Relations weigh in.