What factors influence how easily SARS-CoV-2 is transmitted between individuals?

Bottom Line:

Three factors were shown to decrease how easily SARS-CoV-2 is transmitted across the United States: lower population density, temperate climate and social distancing.


Rubin, D. et al. Association of Social Distancing, Population Density, and Temperature With the Instantaneous Reproduction Number of SARS-CoV-2 in Counties Across the United States. JAMA Network Open (2020). https://doi.org/10.1001/jamanetworkopen.2020.16099

Date Published:

23 July 2020


The R value of a virus, such as SARS-CoV-2, represents the number of people that will become infected with the virus from one individual who is infected. It helps measure how transmissible a virus is (i.e. how quickly it spreads between individuals), and therefore helps predict how an outbreak will evolve. The goal of this study was to determine how the R value of SARS-CoV-2, and therefore its transmissibility, is affected by a variety of factors such as population density, temperature, and social distancing. The researchers selected 211 counties in the United States, representing 55% of the US population across 46 states and the District of Columbia. The data showed that all three of these factors influenced the rate of transmission of SARS-CoV-2, such that lower population density, a temperate climate and higher rates of social distancing reduced the R value of the virus. Of these three measures, implementing social distancing practices had the strongest effect on reducing transmission. This information can help inform policy decision-making in different areas that may be at higher risk of SARS-CoV-2 transmission.

Summary by: Caroline Gregory