Phases of a Pandemic

Whether it's the new coronavirus (COVID-19), swine flu, or smallpox, we hear the word pandemic used in a variety of ways. What does pandemic really mean, and when is the term really warranted?

A pandemic refers to an illness that has spread over several countries or continents, usually affecting a large number of people. It takes into account where it is located and how it is spreading. Most recently, the World Health Organization (WHO) declared COVID-19 a pandemic.

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Verywell / Tim Liedtke

Phases of a Pandemic

The Centers Disease for Disease Control and Prevention (CDC) currently has Pandemic Intervals Framework (PIF) in place for tracking the phases of an influenza pandemic. That framework is being applied to COVID-19.

Phase 1: Investigation Interval

A new type of virus is identified and investigated—in animals or humans anywhere in the world—that is thought to have implications for human health.

Phase 2: Recognition Interval

Increased cases, or clusters of cases, are identified, along with an increased potential for person-to-person transmission.

Phase 3: Initiation Interval

Cases of the virus are confirmed with both efficient and sustained person-to-person transmission.

Phase 4: Acceleration Interval

The new virus infects susceptible people. Public health officials may take measures such as closing schools, encouraging social distancing, and offering antivirals or vaccines—if available.

Phase 5: Deceleration Interval

There is a consistently decreasing rate of cases in the United States.

Phase 6: Preparation Interval

Even after the pandemic has subsided, public health officials continue to monitor the virus and brace for another wave of illness.

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Association for Professionals in Infection Control and Epidemiology. Outbreaks, epidemics, and pandemics - what you need to know.

  2. Centers for Disease Control and Prevention. Pandemic preparedness resources. Updated February 15, 2020.