Does it feel like social distancing is a practice without end? If so, watch this. Our doctors and public health officials have a very specific goal in mind, and it's all to do with one particular number. As part of a new series of Explained by Prime Time focusing on COVID-19, Mark Coughlan and public health experts take you through what the 'r-nought' number is, why it matters, and what you can do to change it.