Marc Lipsitch and his research group study the impact of medical and public health interventions and human immunity on pathogen populations and the consequences of these changes for human health. Within this broad umbrella they consider both ecological effects (modulating the amount of transmission and infection) and evolutionary ones (shaping the genetic composition of the populations of infectious agents). Specific areas of interest include natural selection imposed by strain-specific vaccines and antibiotics, design and evaluation of measures to control outbreaks and pandemics, methods for evaluating vaccine efficacy, and surveillance design.