What Is the Difference Between an Epidemic and a Pandemic?

Brazil Faces New Health Epidemic As Mosquito-Borne Zika Virus Spreads Rapidly
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The words pandemic and epidemic are often associated, and easily confused. However, although somewhat similar, the two words have very different meanings. Thus, some major clarification is necessary.

What is an Epidemic?

An epidemic refers to a contagious, infectious or viral illness that spreads to many people in one specific geographic region. For instance, an outbreak of the swine flu in the United States would be considered an epidemic, as long as the infection is limited to just the United States.

An epidemic occurs in excess of the numbers of cases that would usually be expected of the infection or illness.

What is a Pandemic?

A pandemic differs greatly from an epidemic. Like an epidemic, a pandemic refers to a contagious, infectious or viral illness that spreads. However, unlike an epidemic, a pandemic is not limited to one specific geographic region. Instead, a pandemic has the potential to include millions of people in many areas and countries across the globe, according to the World Health Organization's description.

Phases of a Pandemic

The World Health Organization keeps track of all viruses through a set of phases:

  • Phase 1: During phase 1, viruses circulate within animals only. No human infection has yet resulted from the animal virus.
  • Phase 2: In phase 2, an animal virus has caused an infection in a human being. At this point there is a basic level of pandemic threat because the virus strain has mutated to make that transfer to a human. Humans are now susceptible to the virus.  
  • Phase 3: In phase 3, the virus continues to spread. Groups of human beings have contracted the virus in one community. There is potential for spread of the virus if others outside that community come into contact with those humans who are infected. At this point, the illness may be considered to be an epidemic in that community, but it is not yet pandemic.
  • Phase 4: In phase 4, the virus spreads even more. Human-to-human and animal-to-human virus transmission is causing outbreaks in many communities and more people are getting sick in those communities. More communities report outbreaks and the possibility of a pandemic is becoming more likely, although the development of a pandemic is not yet a guarantee.
  • Phase 5: In phase 5, human-to-human transmission is taking place in at least two countries in one WHO region. WHO has a network of 120 National Influenza Centers in 90 different countries. At phase 5, a majority of countries have not yet been affected, but a pandemic is considered imminent. Phase 5 signifies that governments and health officials must be ready to implement their pandemic mitigation plans.
  • Phase 6: The last stage is stage 6. At stage 6, a global pandemic is underway. Illness is widespread and governments and health officials are actively working to curtail the spread of the disease, and to help their populations deal with it using preventive and stop-gap measures.
  • Post-pandemic: Post-pandemic is the period after the pandemic has occurred. After the increase in activity, the disease-spreading activity will begin to wane. Prevention of a second wave is key at this point.

The time frame of these phases varies greatly, as it could range from months to years.

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