Reduction in mobility and COVID-19 transmission

TLDR

Countries have sought to control SARS‑CoV‑2 transmission by restricting movement through social distancing interventions, reducing contacts. The study characterises the relationship between transmission and mobility for 52 countries worldwide. Mobility data serve as a proxy for social distancing to assess this relationship. Transmission decreased with initial mobility reductions in 73 % of countries, but decoupling occurred after relaxation in 80 %, and mobility explained 48 % of transmissibility variation on average, with predictive power dropping from 74 % pre‑relaxation to 30 % post‑relaxation, yet in countries with a persistent relationship, mobility still associated with lower transmission after relaxation.

Abstract

In response to the COVID-19 pandemic, countries have sought to control SARS-CoV-2 transmission by restricting population movement through social distancing interventions, thus reducing the number of contacts. Mobility data represent an important proxy measure of social distancing, and here, we characterise the relationship between transmission and mobility for 52 countries around the world. Transmission significantly decreased with the initial reduction in mobility in 73% of the countries analysed, but we found evidence of decoupling of transmission and mobility following the relaxation of strict control measures for 80% of countries. For the majority of countries, mobility explained a substantial proportion of the variation in transmissibility (median adjusted R-squared: 48%, interquartile range - IQR - across countries [27–77%]). Where a change in the relationship occurred, predictive ability decreased after the relaxation; from a median adjusted R-squared of 74% (IQR across countries [49–91%]) pre-relaxation, to a median adjusted R-squared of 30% (IQR across countries [12–48%]) post-relaxation. In countries with a clear relationship between mobility and transmission both before and after strict control measures were relaxed, mobility was associated with lower transmission rates after control measures were relaxed indicating that the beneficial effects of ongoing social distancing behaviours were substantial.