Patrick Bardill, Ph.D.:
Generally speaking, there are a few properties of SARS-CoV-2 that contributed to it becoming a pandemic. It is a respiratory virus and easily transmitted through coughing or sneezing. It also appears to usually produce a very mild disease, with some people not realizing they are infected. Those people then interact with other individuals, passing the virus on without realizing they are sick. Finally, SARS-CoV-2 is a new virus for humans, meaning that before the present pandemic, no one had immunity to it from a previous infection.