Quantifying the impact of physical distance measures on the transmission of COVID-19 in the UK

Kevin Van Zandvoort,Kiesha Prem,G James Rubin,Petra Klepac,W John Edmunds,Christopher I Jarvis,Amy Gimma

doi:10.1186/s12916-020-01597-8

Kevin Van Zandvoort, Kiesha Prem + Show 5 more

Open Access

https://doi.org/10.1186/s12916-020-01597-8

Copy DOI

Abstract

BackgroundTo mitigate and slow the spread of COVID-19, many countries have adopted unprecedented physical distancing policies, including the UK. We evaluate whether these measures might be sufficient to control the epidemic by estimating their impact on the reproduction number (R0, the average number of secondary cases generated per case).MethodsWe asked a representative sample of UK adults about their contact patterns on the previous day. The questionnaire was conducted online via email recruitment and documents the age and location of contacts and a measure of their intimacy (whether physical contact was made or not). In addition, we asked about adherence to different physical distancing measures. The first surveys were sent on Tuesday, 24 March, 1 day after a “lockdown” was implemented across the UK. We compared measured contact patterns during the “lockdown” to patterns of social contact made during a non-epidemic period. By comparing these, we estimated the change in reproduction number as a consequence of the physical distancing measures imposed. We used a meta-analysis of published estimates to inform our estimates of the reproduction number before interventions were put in place.ResultsWe found a 74% reduction in the average daily number of contacts observed per participant (from 10.8 to 2.8). This would be sufficient to reduce R0 from 2.6 prior to lockdown to 0.62 (95% confidence interval [CI] 0.37–0.89) after the lockdown, based on all types of contact and 0.37 (95% CI = 0.22–0.53) for physical (skin to skin) contacts only.ConclusionsThe physical distancing measures adopted by the UK public have substantially reduced contact levels and will likely lead to a substantial impact and a decline in cases in the coming weeks. However, this projected decline in incidence will not occur immediately as there are significant delays between infection, the onset of symptomatic disease, and hospitalisation, as well as further delays to these events being reported. Tracking behavioural change can give a more rapid assessment of the impact of physical distancing measures than routine epidemiological surveillance.

Highlights

To mitigate and slow the spread of COVID-19, many countries have adopted unprecedented physical distancing policies, including the Office of National Statistics (UK)
We evaluate whether these measures might be sufficient to control the epidemic by estimating their impact on the reproduction number
If similar changes are observed across the UK population, we would expect the basic reproduction number to be below 1 (0.62; 95% Confidence interval (CI) 0.37–0.89) and that these physical distancing measures will lead to a decline in cases in the coming weeks

Summary

Introduction

To mitigate and slow the spread of COVID-19, many countries have adopted unprecedented physical distancing policies, including the UK. On March 23, with just over 6000 confirmed cases, the UK Government implemented strict physical distancing measures instructing individuals to stay at home and avoid leaving their house except for essential work, to take one form of exercise a day, and to buy essential items such as food and medicines. This followed the closure of sporting events, schools, restaurants, bars, gyms, and other leisure or hospitality-related businesses the previous week [4] and an increase in social distancing among the population that had been taking place for several days before the announcement [5]. One previous survey—conducted in two Chinese cities, Wuhan and Shanghai, in February 2020—quantified the impact of these measures on individuals’ contact patterns during the COVID-19 pandemic [13]

Methods

Results

Discussion

Conclusion