As of November 9, more than 1 million Americans had contracted COVID-19, and if you have read anything related to the virus, you've probably heard the term R_o (Reproduction Number or R Naught). It describes, on average, how many people an infected person is likely to subsequently infect. Mathematically, it's an extremely complex calculation, but at its core, it explains how easily a disease can spread from person to person.

A higher reproduction number means that more people will be infected, while a lower reproduction number means that fewer people will be infected. For instance, an  R_o of 1 means that each infected person subsequently infects one other person. An  R_o of 1.2 means that every person will go on to infect 20% more, and this number will grow exponentially.

The R_o of COVID-19 is not constant across the country. It is influenced by how strictly individuals adhere to social distancing and mask-wearing. The R_o can help leaders understand if outbreaks are spreading or slowing in their communities. Current data shows that the R_o for the coronavirus in the United States is between 1 and 1.5. In some communities, the R_o is 1 or less, which means that the spread of COVID-19 has been controlled or is being controlled in those areas.