R0 / Reproductive Rate

Pronounced “r-naught”.  This is the “basic reproductive number” of a contagious disease: the average number of additional cases that directly result from a single person bringing it into a community. COVID-19 is believed to have an R0 of 2.2-2.7, which means that the first person who has it in a community will likely infect two or three others, and those newly infected people will each go on to infect another two to three people, rapidly spreading the virus.