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

Estimates of regional infectivity of COVID-19 in the United Kingdom following imposition of social distancing measures Background In late 2019 an outbreak of a novel infectious disease was detected. It manifested principally with severe acute respiratory distress, and pneumonia 1 , although many cases followed a mild course 2 . The pathogen was rapidly identified as a new species of coronavirus (severe acute respiratory syndrome coronavirus 2 -SARS-CoV-2), and the disease named COVID-19 3 . Global transmission of the virus followed and major outbreaks have been observed in Europe, beginning with Italy 4 . On the 31st Jan 2020 the first cases were identified in the UK 5 . This was initially managed using testing of suspected individuals in the community, contact tracing and isolation of affected cases. However this was successful only in delaying the spread of the disease and on 13th March 2020 the UK government moved towards a mitigation strategy reserving testing for hospital inpatients only 6 . Following this, a stepwise implementation of social distancing measures were mandated by the government including voluntary self isolation of any symptoms & vulnerable people 7 , a ban on non essential travel worldwide 8 and school closures 9 . Finally on 23rd March 2020 the government mandated that everyone apart from essential workers should stay at home and away from others 10 Epidemiological studies conducted during the outbreak in China have provided us with a number of estimates of the parameters describing the virus's spread through the population including a reproduction number between 2.24 and 3.58 11 and a median incubation period of 5.1 days (credible interval 4.5 to 5.8) 12 . It is estimated that fewer than 2.5% of people will show signs before 2.2 days and 97.5% of people who will develop symptoms will have done so by 11.2 days after exposure 12 .