In epidemiology, an R₀ is a measure of transmission. It basically represents the average number of people that one infected person will, in turn, infect. Based on current information, coronavirus has an R₀ somewhere between 2 and 3, so the average infected person will pass the virus on to two or three more people. That makes it more contagious than the flu, which has an R₀ of about 1.5. Measles, one of the most contagious viruses, has an R₀ of about 15.