County-Level Exposures to Greenness and Associations with COVID-19 Incidence and Mortality in the United States

Background: During the COVID-19 outbreak, green spaces may be a crucial factor to maintain a physically and socially active lifestyle while not increasing risk of infection. We evaluated whether greenness is related to COVID-19 incidence and mortality in the United States. Methods: We downloaded data on COVID-19 cases and deaths for each US county up through June 7, 2020, from Johns Hopkins University, Center for Systems Science and Engineering Coronavirus Resource Center. We used April-May 2020 Normalized Difference Vegetation Index (NDVI) data, to represent the greenness exposure during the initial COVID-19 outbreak in the US. We fitted negative binomial mixed models to evaluate associations of NDVI with COVID-19 incidence and mortality, adjusting for potential confounders. We evaluated whether the associations were modified by population density, proportion of Black residents, median home value, and issuance of stay-at-home order. Findings: An increase of 0·1 in NDVI was associated with a 6% (95% Confidence Interval: 3%, 10%) decrease in COVID-19 incidence rate. Associations with COVID-19 incidence were stronger in counties with high population density and high median home values, and in counties with stay-at-home orders. Greenness was not associated with COVID-19 mortality in all counties; however, it was protective in counties with high percentages of Black residents, high median home value, and higher population density. Interpretation: Exposures to NDVI had beneficial impacts on county-level incidence of COVID-19 in the US and may have reduced county-level COVID-19 mortality rates, especially in densely populated counties. Funding: this study was funded by R01HL150119 and R01ES028033 Declaration of Interests: The authors declare that we have no conflicts of interest.