A pandemic is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. Recent pandemics include tuberculosis, Russian flu, Spanish flu, Asian flu, cholera, Hong Kong flu, HIV/AIDS, SARS and COVID-19.

In the headline question to this series, a global catastrophe is defined as a 10% decrease in the world population in any period of 5 years. On this definition, the COVID-19 pandemic does not count as a global catastrophe.

By contrast, the bubonic plague likely does count as a global catastrophe on that definition, as it is estimated that it killed between 25 million and 200 million people in the space of five years, that is between 5 percent to 40 percent of the world’s population at the time.