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

Our take —

Using survey data, this study showed that in-person contacts dramatically declined following implementation of strict social distancing measures in the UK, to levels that would substantially slow epidemic growth. Participants in this study were recruited by email and may have different contact patterns than the population at large, potentially biasing study conclusions.

Study design

Modeling/Simulation; Cross-Sectional

Study population and setting

A cross-sectional survey was administered through email to adults in the United Kingdom (UK) aged 18 years and older. The survey assessed contact patterns beginning one day after the UK implemented a national lockdown to control SARS-CoV-2 transmission. The lockdown included (1) a stay-at-home order whereby individuals were only allowed to leave the home for essential activities such to buy groceries or medicines and to exercise once per day; (2) closure of schools; (3) closure of restaurants, bars, gyms, and other leisure/hospitality businesses; and (4) a ban on mass gatherings, including sporting events. Social contact patterns were compared before and after the lockdown using data from an earlier study that similarly measured patterns (the POLYMOD survey). Contact data from the current survey were then used to estimate the reproductive number following implementation of the lockdown.

Summary of Main Findings

1,346 individuals participated and reported 3,849 in-person contacts. The mean number of in-person contacts declined from 10.8 per day before the lockdown to 2.9 per day after the lockdown. Most contacts (~58%) after the lockdown were in the home. The estimated reproductive number following the lockdown was 0.62 (95%: 0.37-0.89), well below the epidemic threshold for growth.

Study Strengths

This study directly measured impact of social distancing measures on contact patterns using highly detailed age and gender-specific contact data measured by personal diary. This type of contact data is rare and useful for epidemiological studies. The survey also had good geographic and demographic representation among those who participated.

Limitations

This study surveyed and recruited participants by email; participation in email surveys may be related to contact patterns, which would bias study results. Adolescents and children were excluded from the survey and their contact patterns were imputed. Additionally, contact patterns were measured immediately after implementation of the lockdown. The nature of contacts may change as people become fatigued by lockdown measures or as the incidence of disease rises and falls in the population.

Value added

This study provides some of the first empirical data from Europe documenting the extent to which age-specific contact patterns changed following implementation of strict social distancing measures in response to SARS-CoV-2 transmission.

This review was posted on: 4 May 2020