Clinical informatics focuses at the level of the individual. Work in clinical informatics includes the development of Electronic Medical Records (EMR), Decision Support Systems (DSS), standardized vocabularies for storing medical information, as well as standards for interoperability between different clinical systems.
Public health informatics focuses at the level of populations. This includes computerized disease surveillance systems, vaccine registries, systems for disaster management, and tools to educate patients.
Translational informatics is a newer sub-field that focuses on moving discoveries from the laboratory into routine clinical care faster. Systems to improve clinical research are included in translational informatics.