Weather and COVID-19 Deaths During the Stay-at-Home Order in the U.S.

Background: Understanding if and how weather patterns influence the transmission of SARS-CoV-2 will impact public health preparedness, as the second year of the COVID-19 pandemic draws near. However, the research on weather and SARS-CoV-2 transmission has yielded mixed results. This study aimed to estimate the association of weather and COVID-19 fatality rates during the period of stay-at-home orders in U.S. counties. Methods: This study utilized a county-level longitudinal design to examine COVID-19 adult deaths from the stay-at-home orders to reopening. COVID-19 deaths came from public health departments’ daily reports and considered exposure as the 18 to 22 day-period before death. Further, models included information on state-level social distancing measures, Census Bureau demographic information, daily weather information, and daily air pollution. The primary measures included minimum and maximum daily temperature, precipitation, ozone concentration, PM2·5 concentrations, and U.V. light index. Findings: The average minimum daily temperature threshold of 53 to 63 degrees Fahrenheit (°F was positively associated with COVID-19 deaths. A 1°F increase in the average minimum temperature was associated with 1·9% (95% CI, 0·2%−3·6%) increase in deaths about 20 days later. An ozone concentration increase of one ppb (part per billion) decreased daily deaths by 2·0% (95% CI, 0·1%−3·6%). Ozone levels below 38 ppb appeared negatively correlated with deaths. Interpretation: Increased mobility and contacts may drive the observed association of minimum daily temperature on COVID-19 deaths. The effect of ozone may be related to its disinfectant properties, but this requires further confirmation. Funding Statement: No Funding Received. Declaration of Interests: None to declare.