Every infectious disease has an r0 (pronounced r-nought) value. Since it emerged late last year, specialists have been trying to work out one for Covid-19.
As Professor Mary Horgan, a renowned infectious disease specialist from Kerry and president of the Royal College of Physicians explained to me, the process involves maths, understanding of social patterns, and medical knowledge.
There have been several studies published since January, most put Covid-19's r0 around 2.5. That means a typical person who is infected by the disease will spread it to 2.5 - two or three - other people during the period they're infected.
For the scientists, it's broadly good news is when someone infected has passed it to fewer people than the r0, but the wider