Pandemics are a lot like wildfires—first they spark, and then they spread. New infectious diseases can arise from anywhere. They are often triggered by human activities such as changes in land use or agriculture. Once a new disease emerges, it can spread quickly, pushed along by human travel and commerce.
The virus that causes COVID-19 was first identified in China in December 2019. Because of its unique characteristics and our interconnected society, the virus rapidly spread across the globe.