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Protecting the public is a core function of the government. Usually, this function is thought of as a national security or military defense mission, but protecting the public from health threats is also a security function. Because large-scale health emergencies can cause loss of life and loss of confidence in government capacities, preparing for and responding to health emergencies is increasingly seen as an element of national security.1,2

Health emergencies have affected human society at least since the classical civilizations of Rome and Greece. For example, the Greek city-states of Athens and Sparta experienced a plague, of unknown cause, during the Peloponnesian War (431–404 BC). In 541 AD, the bacterium Yersinia pestis caused severe social disruption and widespread mortality in the Byzantine (Eastern Roman) Empire. During the fourteenth to eighteenth centuries, recurrent waves of the “Black Death” pandemics, caused by Yersinia pestis, occurred throughout Europe.3 Events like the yellow fever outbreaks in Philadelphia in 1793 and in Memphis in 1878 similarly caused widespread death and destruction.4 Large-scale natural disasters, such as droughts, earthquakes, volcanic eruptions, and floods have also led to the collapse of cities, and at times entire civilizations. For example, one leading theory is that a massive drought, potentially exacerbated by human deforestation, led to the collapse of the Mayan empire in Central America and Southern Mexico during the ninth-century AD.5 All these events are more notable for the destruction they caused, and the sense of inevitability, than any semblance of an effective public health response. Today, advances in communication, organizational capacity, the logistical capacity to move resources at speed and scale, and scientific advances in diagnostics, vaccines, and therapeutics have created the capability to respond effectively to large-scale emergencies and mitigate their consequences in ways that in the past would have been unthinkable.


Public health emergencies can be defined as events that overwhelm the available capacity to respond. In the modern era, three types of public health emergencies, each requiring a distinct type of response, can be distinguished. These are natural disasters, which are predictable based on the historical record; manmade events (emergencies that are the result of human action, either intentional or accidental); and emerging threats caused by an unexpected or novel agent that leads to an unanticipated or unimagined severe epidemic or pandemic. Effective response to each of these requires systems that match the speed and scale of the response with the speed and scale of the emergency.

Natural disasters, such as hurricanes, earthquakes, tornadoes, flood, and tsunamis, typically cause destruction of physical infrastructure, and the severity of the event is directly related to the magnitude of this destruction. Government emergency response agencies (in the United States, e.g., the Federal Emergency Management Agency or FEMA) typically lead responses to these emergencies. These events can be considered “predictable” or anticipated events, as the season ...

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