Zhou X et al., Excess of COVID-19 cases and deaths due to fine particulate matter exposure during the 2020 wildfires in the United States
Science Advances  13 Aug 2021: Vol. 7, no. 33, eabi8789. DOI: 10.1126/sciadv.abi8789

https://advances.sciencemag.org/content/7/33/eabi8789      https://www.nytimes.com/2021/08/13/climate/wildfires-smoke-covid.html

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Exposure to smoke, whether from air pollution or cigarette smoke, is believed to impair the function of white blood cells in the lungs, blunting the body’s immune response. The chemicals in particulate matter can also inflame cells lining the airways and lungs. In both cases, if the body is exposed to a virus in addition to air pollution, the immune response may be slowed and the person may develop a more severe illness than they would have otherwise, researchers say.

The findings build on the well-established connection between air pollution and respiratory-tract infections and conditions such as asthma. But the study is the first to show a statistical link between wildfire smoke and Covid-19 caseloads and deaths. …”