Weather, air pollution, and SARS-CoV-2 transmission: a global analysis

Ran Xu; Hazhir Rahmandad; Marichi Gupta; Catherine DiGennaro; Navid Ghaffarzadegan; Heresh Amini; Mohammad S Jalali

doi:10.1016/S2542-5196(21)00202-3

Weather, air pollution, and SARS-CoV-2 transmission: a global analysis

Lancet Planet Health. 2021 Oct;5(10):e671-e680. doi: 10.1016/S2542-5196(21)00202-3.

Authors

Ran Xu¹, Hazhir Rahmandad², Marichi Gupta³, Catherine DiGennaro³, Navid Ghaffarzadegan⁴, Heresh Amini⁵, Mohammad S Jalali⁶

Affiliations

¹ Department of Allied Health Sciences, University of Connecticut, Storrs, CT, USA.
² Sloan School of Management, Massachusetts Institute of Technology, Cambridge, MA, USA.
³ Institute for Technology Assessment, Massachusetts General Hospital, Boston, MA, USA.
⁴ Department of Industrial and Systems Engineering, Virginia Tech, Falls Church, VA, USA.
⁵ Department of Public Health, University of Copenhagen, Copenhagen, Denmark; Department of Environmental Health, Harvard T H Chan School of Public Health, Boston, MA, USA.
⁶ Institute for Technology Assessment, Massachusetts General Hospital, Boston, MA, USA; MGH Institute for Technology Assessment, Harvard Medical School, Harvard University, Boston, MA, USA. Electronic address: msjalali@mgh.harvard.edu.

Abstract

Background: Understanding how environmental factors affect SARS-CoV-2 transmission could inform global containment efforts. Despite high scientific and public interest and multiple research reports, there is currently no consensus on the association of environmental factors and SARS-CoV-2 transmission. To address this research gap, we aimed to assess the relative risk of transmission associated with weather conditions and ambient air pollution.

Methods: In this global analysis, we adjusted for the delay between infection and detection, estimated the daily reproduction number at 3739 global locations during the COVID-19 pandemic up until late April, 2020, and investigated its associations with daily local weather conditions (ie, temperature, humidity, precipitation, snowfall, moon illumination, sunlight hours, ultraviolet index, cloud cover, wind speed and direction, and pressure data) and ambient air pollution (ie, PM_2·5, nitrogen dioxide, ozone, and sulphur dioxide). To account for other confounding factors, we included both location-specific fixed effects and trends, controlling for between-location differences and heterogeneities in locations' responses over time. We built confidence in our estimations through synthetic data, robustness, and sensitivity analyses, and provided year-round global projections for weather-related risk of global SARS-CoV-2 transmission.

Findings: Our dataset included data collected between Dec 12, 2019, and April 22, 2020. Several weather variables and ambient air pollution were associated with the spread of SARS-CoV-2 across 3739 global locations. We found a moderate, negative relationship between the estimated reproduction number and temperatures warmer than 25°C (a decrease of 3·7% [95% CI 1·9-5·4] per additional degree), a U-shaped relationship with outdoor ultraviolet exposure, and weaker positive associations with air pressure, wind speed, precipitation, diurnal temperature, sulphur dioxide, and ozone. Results were robust to multiple assumptions. Independent research building on our estimates provides strong support for the resulting projections across nations.

Interpretation: Warmer temperature and moderate outdoor ultraviolet exposure result in a slight reduction in the transmission of SARS-CoV-2; however, changes in weather or air pollution alone are not enough to contain the spread of SARS-CoV-2 with other factors having greater effects.

Funding: None.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Air Pollution* / adverse effects
COVID-19* / epidemiology
COVID-19* / transmission
Global Health* / statistics & numerical data
Humans
Pandemics
SARS-CoV-2
Weather*