Do Social Distancing and Weather Affect SARS-CoV-2 Transmission?

The findings:

At the county level, social distancing, spring-like temperatures and lower population density were associated with a decrease in transmission of SARS-CoV-2, the virus that causes COVID-19. Social distancing, which the researchers measured as changes in travel to non-essential businesses over time, appeared to have the most significant effect on reducing transmission. Specifically, a 50 percent decrease in visits to non-essential businesses was associated with a 45 percent decrease in the reproduction number, or the estimated number of people who will be infected for every one COVID-19 case.

Why it matters:

SARS-CoV-2 has caused a worldwide pandemic. According to the World Health Organization, as of July 22, there have been almost 15 million cases and more than 600,000 deaths globally. The pandemic led to the implementation of social distancing measures across the United States and around the world. Most models of COVID-19 projections have considered large areas, such as countries and states. This model is unique in producing short-term projections at the county level.

Who conducted the study:

Researchers at PolicyLab at Children’s Hospital of Philadelphia conducted the study, led by David Rubin, MD, MSCE, director of PolicyLab, Jing Huang, PhD, assistant professor in the Department of Biostatistics, Epidemiology, and Informatics at the University of Pennsylvania Perelman School of Medicine, and Gregory Tasian, MD, MSc, MSCE, associate professor in the Department of Biostatistics, Epidemiology, and Informatics at the University of Pennsylvania Perelman School of Medicine, as well as attending urologist at CHOP.

How they did it:

The researchers conducted an observational study using data from February 25 to April 23, 2020, in 211 counties, which represented state capitals and cities of at least 100,000 people in 46 states and the District of Columbia. They measured social distancing using daily cellphone movement, obtained U.S. Census data to determine population density, and wet-bulb temperatures from the National Oceanic Atmospheric Administration Local Climatological Data.

Quick thoughts:

“Our data reveal that if the United States had collectively waited longer, opened more slowly, and then kept our gathering sizes small, we might have reduced case counts like Europe or Canada, and experienced a relatively normal summer, free of extreme disease burden from COVID-19,” Dr. Rubin said. “As the pandemic resurgence continues, we must commit to social distancing and universal masking nationwide in order to gain control of this epidemic and avoid a potentially catastrophic fall and winter season.”

What’s next:

PolicyLab analyzes the data weekly, then publishes the data and projections on its website. Using these data, PolicyLab continues to inform state and local policymakers in their response to reopening society.

Where the study was published:

The study appeared in JAMA Network Open.

Where to learn more:

Visit the PolicyLab press release.