Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries

Abstract

Objective: To evaluate the association between physical distancing interventions and incidence of coronavirus disease 2019 (covid-19) globally.

Design: Natural experiment using interrupted time series analysis, with results synthesised using meta-analysis.

Setting: 149 countries or regions, with data on daily reported cases of covid-19 from the European Centre for Disease Prevention and Control and data on the physical distancing policies from the Oxford covid-19 Government Response Tracker.

Participants: Individual countries or regions that implemented one of the five physical distancing interventions (closures of schools, workplaces, and public transport, restrictions on mass gatherings and public events, and restrictions on movement (lockdowns)) between 1 January and 30 May 2020.

Main outcome measure: Incidence rate ratios (IRRs) of covid-19 before and after implementation of physical distancing interventions, estimated using data to 30 May 2020 or 30 days post-intervention, whichever occurred first. IRRs were synthesised across countries using random effects meta-analysis.

Results: On average, implementation of any physical distancing intervention was associated with an overall reduction in covid-19 incidence of 13% (IRR 0.87, 95% confidence interval 0.85 to 0.89; n=149 countries). Closure of public transport was not associated with any additional reduction in covid-19 incidence when the other four physical distancing interventions were in place (pooled IRR with and without public transport closure was 0.85, 0.82 to 0.88; n=72, and 0.87, 0.84 to 0.91; n=32, respectively). Data from 11 countries also suggested similar overall effectiveness (pooled IRR 0.85, 0.81 to 0.89) when school closures, workplace closures, and restrictions on mass gatherings were in place. In terms of sequence of interventions, earlier implementation of lockdown was associated with a larger reduction in covid-19 incidence (pooled IRR 0.86, 0.84 to 0.89; n=105) compared with a delayed implementation of lockdown after other physical distancing interventions were in place (pooled IRR 0.90, 0.87 to 0.94; n=41).

Conclusions: Physical distancing interventions were associated with reductions in the incidence of covid-19 globally. No evidence was found of an additional effect of public transport closure when the other four physical distancing measures were in place. Earlier implementation of lockdown was associated with a larger reduction in the incidence of covid-19. These findings might support policy decisions as countries prepare to impose or lift physical distancing measures in current or future epidemic waves.

Fig 1

Physical distancing policies implemented by countries globally. Country codes used are based on the Alpha-3 codes by International Organization for Standardization (see appendix, pp4-5)

Fig 2

Pairwise meta-analysis on the association between physical distancing interventions and change in incidence of coronavirus disease 2019. Effects are reported as incidence rate ratios (95% confidence intervals). I²=an estimate of the percentage of total variation across the countries that is due to heterogeneity rather than chance. Country codes used are based on the Alpha-3 codes by International Organization for Standardization (see appendix, pp4-5)

Fig 3

Association between the combinations of physical distancing interventions and change in incidence of coronavirus disease 2019. I²=an estimate of the percentage of total variation across the countries that is due to heterogeneity rather than chance

Fig 4

Association between the sequence of physical distancing interventions and change in incidence of coronavirus disease 2019. I²=an estimate of the percentage of total variation across the countries that is due to heterogeneity rather than chance