Wildfires are burning on an unprecedented level in the western United States, and Covid-19 cases are surging at the same time. A new study shows a link between exposure to wildfire smoke and increased susceptibility to Covid-19 and its respiratory symptoms. In the study, which was published in the online journal Science Advances, scientists used publicly available daily data on fine particulate matter (PM 2.5) from last year and the number of Covid cases and deaths to link the two sets of data.
Last year, over 10 million acres were burned in the western United States. Wildfires produce high levels of PM 2.5, the pollutant in smoke that poses the greatest health risk. Exposure to wildfire smoke and PM 2.5 has long been known to exacerbate respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Since the novel coronavirus causes a respiratory disease, PM 2.5 exacerbates the symptoms in a similar manner.
The study’s authors found that the daily Covid-19 infection and death rates were higher on wildfire days compared to non-wildfire days. They looked at 92 counties in California, Oregon, and Washington that experienced wildfires in 2020. They used satellite images of the fires and public data on Covid rates to conclude that in most of the counties they studied, there was strong evidence that higher levels of smoke and soot led to higher rates of Covid infections and deaths. When PM 2.5 levels remained high for more than 28 consecutive days, Covid cases increased by nearly 12% and deaths by over 8%.
Additionally, a separate review by another group of scientists found that the co-occurrence of Covid-19 infection and wildfire smoke inhalation may present an increased risk for Covid-19. Exposure to air pollution while Covid-positive causes the body to respond with an allergic immune response rather than an antiviral response. This may have an adverse effect on Covid severity and outcomes.
Other studies have shown that short term exposure to wildfire smoke leads to an increase in emergency room visits and subsequent hospitalizations. In short, PM 2.5 from wildfires nearly always has a negative effect on the health of those who are exposed to it.
The study’s authors acknowledge that new Covid-19 cases and deaths can fluctuate for reasons other than short-term exposure to PM 2.5. Changes in the temperature, humidity levels, and implementation of disease prevention measures such as social distancing and mask wearing could also impact the link between infections rising on wildfire days. They adjusted for both measured and unmeasured confounding factors to control for seasonality and trends.
Climate change and a warming earth are also cited as contributing factors to the recent increase in catastrophic wildfires. A combination of global warming, increased wildfires, and Covid-19 will be used as reasons for the need for emergency measures to fight climate change.
