While the US was contending with the COVID-19 pandemic, huge wildfires that swept across the country in 2020 may have contributed to thousands of COVID cases and deaths, according to a US study on fine particulate matter (PM 2.5) air pollution from wildfires and COVID-19. 

The study, conducted by researchers at the Harvard Chan School of Public Health, found that the cumulative total of COVID-19 cases and deaths attributable to daily increases in PM 2.5 from wildfires was 19,700 and 750, respectively.

Wildfires produce high levels of fine particulate matter, which has been linked to several negative health outcomes, including premature death, asthma, chronic obstructive pulmonary disease, and other respiratory illnesses.

The study used monitoring data on PM 2.5 air concentrations at a county- and daily-levels, wildfire satellite data, and the number of COVID-19 cases and deaths in 92 countries, representing 95% of the population across California, Oregon, and Washington – three states that bore the brunt of the 2020 wildfires.  

“The convergence of the pandemic and wildfires across the western US,” noted Francesca Dominici, senior author of the study at the Harvard Chan School, has brought “unimaginable challenges in public health.” 

“In this study, we are providing evidence that climate change – which increases the frequency and the intensity of wildfires – and the pandemic are a disastrous combination,” added Dominici. 

‘Hazardous’ levels of fine particulate matter attribute to increased cases and death 

Several counties in the three states experienced levels of PM 2.5 deemed “hazardous” by the US Environmental Protection Agency. High levels of PM 2.5 were attributable to a substantial percentage of total COVID-19 cases and deaths in these areas.

Researchers found that wildfires amplified the effect of exposure to fine particulate air pollution on COVID-19 cases and deaths, up to four weeks after the exposure. On average, a daily increase of PM 2.5 was associated with an 11.7% increase in COVID-19 cases and an 8.4% increase in COVID-19 deaths.

Looking at individual wildfire days and at individual counties, they found that Butte, California and Whitman, Washington, had the highest percentage of total COVID-19 cases attributable to high levels of PM 2.5, 17.3% and 18.2% respectively. 

Two counties in California, Butte and Calaveras, also had the highest percentage of COVID-19 deaths attributed to high levels of PM 2.5 during wildfires – 41% and 137.4% respectively.

Cascading effect of climate change on health 

The link between COVID-19 and the PM 2.5 released from wildfires is further supported by a recent major report by the Intergovernmental Panel on Climate Change (IPPC) that confirms climate change as an existential health problem that overshadows all others. 

Dominici hopes that this study will prompt policymakers to take urgently needed action. 

“Climate change will likely bring warmer and drier conditions to the West, providing more fuel for fires to consume and further enhancing fire activity. This study provides policymakers with key information regarding how the effects of one global crisis—climate change—can have cascading effects on concurrent global crises—in this case, the COVID-19 pandemic,” she said.   

Image Credits: Daria Devyatkina/Flickr.