Estimates of regional infectivity of COVID-19 in the United Kingdom following imposition of social distancing measures

Robert J Challen; Krasimira Tsaneva-Atanasova; Martin Pitt; Tom Edwards; Luke Gompels; Lucas Lacasa; Ellen Brooks-Pollock; Chris Martin; Gareth Griffith; Leon Danon

In the last part of our analysis we look at the rate of change in R(t) estimated using a simple linear regression. We calculated a regional estimate of the current rate of change of R(t), by fitting a linear equation to the last 10 points, and extracting the derivative of R(t), associated confidence intervals and measures of goodness of fit. Figure 1 shows the time dependence of the reproductive index of SARS-CoV-2 in different regions of the UK. The value of R(t) is within the estimates described in other countries 11 (2.24 to 3.58) and is seen in all regions to be decreasing overall. R(t) remains above or equal to 1 at all times and hence within the region of exponential growth of COVID-19 cases. Over the period from March 19th to March 25th it is notable that, whilst decreasing in England, the reproductive index rose in Northern Ireland, Scotland and Wales before falling again. On the 8th April the R(t) was close to one in all regions apart from England. Two significant dates are marked on the time series. Firstly, the recommendation for specific social isolation of the vulnerable on the 16th March, and secondly, the widespread order to remain at home on the 23rd March. These dates represent the initial and final dates of implementation of social restrictions. The date of one serial interval post-lockdown is also shown.