Weather, Social Distancing, and the Spread of COVID-19

Abstract

Using high-frequency panel data for U.S. counties, I estimate the full dynamic response of COVID-19 cases and deaths to exogenous movements in mobility and weather. I find several important results. First, holding mobility fixed, temperature is found to have a negative and significant effect on COVID-19 cases from 1 to 8 weeks ahead and on deaths from 2 to 8 weeks ahead. Second, holding weather fixed, mobility is found to have a large positive effect on subsequent growth in COVID-19 cases and deaths. The impact on cases becomes significant 3 to 4 weeks ahead and continues through 8 to 10 weeks ahead. The impact on deaths becomes significant around 4 weeks ahead and persists for at least 10 weeks. Third, I find that the deleterious effects of mobility on COVID-19 outcomes are far greater when the local virus transmission rate is above one – evidence supportive of public health policies aiming to reduce mobility specifically in places experiencing high transmission rates while relaxing restrictions elsewhere. Fourth, I find that the dynamic effects of mobility on cases are generally similar across counties, but the effects on deaths are higher for counties with older populations and, surprisingly, counties with lower black or hispanic population shares. Lastly, I find that while the marginal impact of mobility changes has been stable over recent weeks for cases, it has come down for deaths. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial Study is not a clinical trial. ### Funding Statement No external funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: No IRB approval required. Study does not use data on individual human subjects. Study uses county level aggregate data. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data used in the study were obtained from publicly available online sources, which are documented in the paper.