Social restrictions mitigate the impacts of city density and connectivity on global COVID-19 outbreaks.

The COVID-19 pandemic is generally devastating in densely populated cities, and disparate observations of city characteristics on COVID-19 have been reported. In order to unraveling the nexuses of city characteristics and infectious transmissions, this study examined the effects of non-pharmaceutical factors on COVID-19 transmission rates in 180 cities worldwide, during the "first wave" of pandemic when no vaccines were widely available. City density and connectivity significantly increased COVID-19 case and mortality rates. However, their determining roles and influence pathways were continent-dependent and contingent upon social restrictions, and can be significantly mitigated under circumstances of only prompt and rigorous restrictions.. In addition, a metric-dependent effects were observed when validating with population density metrics calculated from different definitions. While socio-economically developed cities likely have high capacity of testing and contact tracing, and global connectedness, it also reflected more resources and infrastructures for social distancing and healthcare. These findings suggest that while city density and connectivity exacerbate infectious spread, forward-looking city planning and effective governance is a promising alternative towards to pandemic mitigation and a sustainable city in an urbanization era. • City density and connectivity increase COVID-19 transmission globally. • Effect of density and connectivity varying and is continent-dependent. • Effect of population density is associated with definitions and data sources. • Socio-economics has mixed effects as their multiple indicative meanings. • Only prompt and rigorous restrictions mitigate infectious transmission. [ABSTRACT FROM AUTHOR]