What Is a Pandemic?

A pandemic occurs when a contagious disease spreads worldwide. A disease that causes a pandemic is typically new (or novel), meaning that people do not have natural immunity to fight it. Because of this, the disease can rapidly spread around the world, infecting many people.

A pandemic is a specific type of epidemic. An epidemic is a sudden increase in the number of cases of a disease in a specific area or region. A pandemic is an epidemic that has spread over several countries or continents, affecting a percentage of the population.

What are the phases of a pandemic?

The World Health Organization (WHO) is responsible for declaring a pandemic.
The WHO classifies a pandemic according to how the spread of the illness fits into the following six phases:

• Phase 1: Viruses that circulate among groups of animals but are not known to transmit to humans. They carry a very small risk of creating a pandemic.
• Phase 2: A new animal virus has been transmitted from animals to humans. This signals the potential risk of a pandemic.
• Phase 3: The animal virus has been transmitted to a group of humans, but human-to-human transmission is nonexistent or extremely low.
• Phase 4: Human-to-human transmission has occurred, causing community outbreaks. This signals a high risk of a pandemic developing.
• Phase 5: The virus has been transmitted in at least two countries. A global pandemic is inevitable.
• Phase 6: The virus has been transmitted in at least one additional country (beyond the two countries in phase 5). A global pandemic is occurring.

Are pandemics common?

Pandemics are often caused by an influenza virus. An influenza pandemic strikes approximately every 10 to 50 years. The COVID-19 pandemic declared on March 11, 2020, is the first pandemic known to be caused by a coronavirus. Coronaviruses are a family of viruses that cause respiratory illnesses, such as the common cold and severe acute respiratory syndrome (SARS).

Preparing for a pandemic

To prepare for a pandemic, individuals should pay attention to updates from the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), have a two-week supply of food and medications available, and make a “plan of care” in the event that illness occurs.