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Distancing Tied to 13% Drop in COVID-19 Incidence in 149 Countries
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Mark Mascolini
Meta-analysis of data from 149 countries determined that implementing any physical distancing measure lowered COVID-19 incidence (the new-infection rate) by 13% [1]. When countries combined 4 measures, COVID-19 incidence fell by 15%. Earlier lockdowns (restricting movement) cut COVID-19 incidence more than later lockdowns.
How much physical distancing measures impede spread of COVID-19 remains uncertain. Partly because of this uncertainty, individual states in the United States and individual countries have set their own course in deciding whether and when to institute physical distancing (often called social distancing), when to relax distancing guidelines, and which specific distancing measures to use.
To address these questions, researchers from the University of Oxford and other UK and US institutions conducted this natural experiment using interrupted time series analysis and synthesizing results with meta-analysis. The research team included countries or regions that adopted any 1 of 5 physical distancing interventions between January 1 and May 30, 2020: closing schools, closing workplaces, closing public transport, restricting mass gatherings and public events, and restricting movement (lockdowns). Country or regional data on COVID-19 incidence came from the European Centre for Disease Prevention and Control, while physical distancing dates came from the Oxford COVID-19 Government Response Tracker.
The investigators figured incidence rates ratios (IRRs) before and after distancing measures using data to May 30, 2020 or 30 days after the intervention ended, whichever came first. Statisticians used random effects meta-analysis to synthesize IRRs across countries.
The analysis involved 149 countries that instituted at least one distancing measure and had incidence data for at least 7 days after the intervention ended. All but 2 countries implemented at least 3 of the 5 measures by May 30, 2020. A pooled estimate of data from all 149 countries figured that instituting any 1 of the 5 distancing measures decreased COVID-19 incidence 13% (IRR 0.87, 95% confidence interval 0.85 to 0.89, P < 0.001). COVID-19 incidence dropped about as much in countries that adopted 4 distancing measures (15%) as in countries that adopted all five (13%). Adopting only 3 interventions lowered incidence by 12%, though that estimate rests on data from only 4 countries.
In 32 countries that combined closing schools, closing workplaces, restricting mass gatherings, and ordering lockdowns, adopting all 4 measures lowered COVID-19 incidence 13%. In 72 countries that added stopping public transport to the other 4 measures, doing so lowered COVID-19 incidence by only an additional 2%.
The sequence in which countries implemented interventions had no consistent impact on COVID-19 incidence. But this analysis did find that starting lockdowns earlier rather than later cut incidence by an additional 4% (IRR 0.86 in 105 countries vs 0.90 in 41 countries).
Overall, physical distancing measures reined in COVID-19 incidence most in countries with higher income (gross domestic product per capita), an older population (higher proportion 65 or older), and stronger pandemic preparedness (country health security index).
The authors caution that their study provides only βa rapid and relatively crude assessment of physical distancing at a relatively early stage of the COVID-19 pandemic.β As the pandemic continues, they advise, βit will be crucial to repeat and extend this analysis to assess the impacts of interventions in the longer term, as well as to study combinations and sequence of the lifting of physical distancing restrictions.β
Reference
1. Islam N, Sharp SJ, Chowell G, et al. Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries. BMJ. 2020 Jul 15;370:m2743. https://doi.org/10.1136/bmj.m2743
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