Published 31 March 2020
Q: How will we know when we have taken back control from Covid-19? A: "R0" (the rate of reproduction of the disease) drops below 1. The math of this is intriguing*, but what it means is that someone catching the disease spreads it to fewer people, and the disease will stop spreading. We can then go back to normality (eventually)... The chart below, which came highly recommended to me, is an excellent way of showing this graphically (for publicly available data).
China is the most advanced in responding to the disease. Most would agree it has taken back a lot of control, and this is visible in the publicly available data. I also understand factories have started to reopen. The situation in China is in complete contrast to the situation in the US, and it is entirely unclear what pressure their health system will face and how it will cope in the coming days. Italy also appears to have started turning the corner and has for the past four days reported fewer new daily cases. Deaths should follow, although with a lag. Hopefully, the UK will follow Italy in the next few days, although it is not currently showing evidence of slowing down - despite evidence of social distancing. So peak admissions are likely to be around the 8th of April - three days later than we previously expected. The question for the UK is how it will manage the transition from the current crisis to a steady-state, which allows the health system to function effectively and people to start to return to work.
* The coefficient on the log of new cases against the log of cumulative cases is R. When R = 1 (South Korea, Italy) the line in the chart is horizontal. When R>1 (US) the line in the chart is upward sloping. When R<1 the line in the chart is downward sloping (China). R cannot be below 0.