Health Alert Network (HAN) is the early warning system run by the Center for Disease Control (CDC). It is a component of the Public Health Information Network (PHIN).
The HAN messaging system uses a variety of communication tools , including email, broadcast faxes, television and phone calls, to alert local, state and federal authorities and the media about urgent health threats and necessary actions. PHIN enables local health officials nationwide to instantaneously access and share disease reports, response plans, and CDC diagnostic and treatment guidelines. The goal is to ensure that each community has rapid and timely access to emergent health information; access to a cadre of highly-trained professional personnel; and evidence-based practices and procedures for effective public health preparedness, response and service on a 24/7 basis.
You can learn more about HAN at the CDC website.