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

There are several significant dates of both social distancing measures, and methodological changes, presented in this analysis. In interpreting the relationship between the dates and changes in the reproductive index we must remember that changes in reproductive index will lag the introduction of a social measure by at least the incubation period of SARS-CoV-2 (median 5.1 days -95% IQR 2.2-11.2) 12 . Given the testing strategy that is currently in place, COVID-19 cases will not be identified until a patient is admitted to hospital with symptoms, the test is performed and results obtained. This introduces further time delays which may vary in length from individual to individual. The delay between onset of symptoms and admission has been estimated at 5 to 9 days 28 . The delay induced by the test processing is unknown. If we assume a 2 day delay for testing, we would estimate that interventions begin to have an effect from 9 days after the intervention, have half of their impact in 14 days, and begin to have full impact after 22 days.