What is a pandemic?
One-line takeaway
BLUF: A pandemic is an epidemic of an infectious disease that has spread across a very large region (typically worldwide), affecting a substantial proportion of the population.
A fundamental explanation of what is a pandemic?
The Explanation
A pandemic is an epidemic of an infectious disease that has spread across a very large region (typically worldwide), affecting a substantial proportion of the population. It implies sustained person-to-person transmission on multiple continents. For example, the 1918 influenza and recent COVID-19 outbreaks were pandemics. The key is large geographic spread and high case numbers – not just severity. Unlike routine outbreaks, a pandemic means the disease is new or resurging globally. Epidemiologists monitor factors like transmissibility and immunity, but by definition a pandemic is a widespread, often novel, epidemic across countries.