The response to the COVID-19 pandemic in the United States varied greatly by jurisdiction. Some counties declared strict stay-at-home orders in the spring of 2020, while neighboring counties took a more relaxed approach to mitigating the spread of the virus. The prevailing wisdom is that this patchwork approach ultimately hindered efforts to suppress virus transmission. If restaurants are closed in one county but remain open in a neighboring jurisdiction, won’t people simply cross the border to go out to eat? However, a study led by researchers at the Johns Hopkins University found a surprising result. They discovered that stay-at-home orders in one county inspired residents of neighboring counties to travel less— even though their home county had more lax regulations. 

The researchers, Vadim Elenev, Luis E. Quintero, Alessandro Rebucci and Emilia Simeonova professors at The Johns Hopkins Carey Business School, examined county-wide stay-at-home orders issued between March 16 and April 7, 2020. They separated counties into those which imposed such restrictions, neighboring counties which did not, and “hinterland” counties which bordered the unrestricted counties but not those with stay-at-home orders. The researchers tracked mobile phone location data to see how much residents of each area traveled and where they went. They found that not only did stay-at-home orders sharply curtail the movements of people in the affected county, but also cut by one-third the mobility of those in adjacent counties. This effect was particularly pronounced in areas that share a media market, indicating that health messages about the necessity of social distancing reached beyond the county with the stay-at-home order. The study was published in the National Bur

The researchers, whose work was funded by the Hopkins Business of Health Initiative, concluded that a staggered approach to stay-at-home orders is more beneficial than a blanket order due to “the additional layers of informational treatment that increases voluntary social distancing.” They also note that these spillover effects should be carefully considered and accounted for by other researchers examining the efficacy of virus prevention measures.