Estimating the impact of physical distancing measures in containing COVID-19: an empirical analysis
Authors: Koh Wee Chian , Naing Lin , Wong Justin 
Published: June 2020

Background

Epidemic modelling studies predict that physical distancing is critical in containing COVID-19. However, few empirical studies have validated this finding. Our study evaluates the effectiveness of different physical distancing measures in controlling viral transmission.

Methods

We identified three distinct physical distancing measures with varying intensity and implemented at different times—international travel controls, restrictions on mass gatherings, and lockdown-type measures—based on the Oxford COVID-19 Government Response Tracker. We also estimated the time-varying reproduction number (Rt) for 142 countries and tracked Rt temporally for two weeks following the 100th reported case in each country. We regressed Rt on the physical distancing measures and other control variables (income, population density, age structure, and temperature) and performed several robustness checks to validate our findings.

Findings

Complete travel bans and all forms of lockdown-type measures have been effective in reducing average Rt over the 14 days following the 100th case. Recommended stay-at-home advisories and partial lockdowns are as effective as complete lockdowns in outbreak control. However, these measures have to be implemented early to be effective. Lockdown-type measures should be instituted two weeks before the 100th case and travel bans about a week before detection of the first case.

Interpretation

A combination of physical distancing measures, if implemented early, can be effective in containing COVID-19—tight border controls to limit importation of cases, encouraging physical distancing, moderately stringent measures such as working from home, and a full lockdown in the case of a probable uncontrolled outbreak.

Research in context

Evidence before this study

Evidence on the impact of physical distancing measures on containing COVID-19 has primarily relied on epidemic modelling studies. As cases accumulate worldwide, it has become possible to use empirical data to validate the model-based findings. The few empirical studies that analyze global case data find that lockdowns and international travel restrictions are important, but have not explored, beyond these broad findings, the intensity and timeliness of the various measures to inform policymaking.

Added value of this study

We assessed, at a normalized stage of the epidemic curve, how the intensity and implementation timing of various physical distancing measures in 142 countries affect viral transmission, measured by the time-varying reproduction number (Rt). Other similar empirical studies treat the measures as binary variables, do not address the potential confounding effect of increased caseload on transmission, and do not use Rt as the primary metric.

Implications of all the available evidence

Our results support the findings in modelling studies, and subsequent empirical studies, that physical distancing measures can limit disease spread. We found that full border control and complete lockdowns are effective, but less stringent measures such as stay-at-home recommendations and working from home are as effective. As such, the framing of lockdown measures as a binary approach may be counterproductive. Overall, these measures are only effective if they are implemented early.