RT @trishgreenhalgh
Transmission of Sars-CoV-2: light blue is from pre-symptomatic people; dark green from asymptomatic. Light green - environmental. Only 40% of transmission is from symptomatic people. Might be a good idea to encourage face coverings in crowded places.

https://science.sciencemag.org/content/early/2020/04/09/science.abb6936.full