Basic estimation-prediction techniques for Covid-19, and a prediction for Stockholm

Tom Britton

The interpretation is that each infectious individual at time t has on average λ infectious contacts per day, and with probability s t /N each such contact results infection. Those susceptibles who get infected move to the infectious state. The other transition is for an infectious individual to stop being infectious and recovering and becoming immune (a few also die). The number of individuals who have recovered (also including the few who die) equals N − s t − i t . This system can be iterated forward sequentially until the first time T when the number of infectious individuals drops below 1: i T ≤ 1 (it never reaches exactly 0 but asymptotes to 0). The number of individuals who have been infected by t equals N − s t .