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Thousands of COVID-19 cases linked to wildfires

Fine particle pollution from wildfire smoke may have been responsible for excess COVID-19 cases and deaths in the United States, according to a new study from the Harvard T.H. Chan School of Public Health

The researchers found a potential link between wildfire-related PM2.5 levels and thousands of COVID-19 cases that occurred between March and December of 2020in California, Oregon, and Washington. 

The study is the first of its kind to investigate the extent to which higher levels of PM2.5 pollution during 2020 wildfires contributed to the COVID-19 pandemic. 

“The year 2020 brought unimaginable challenges in public health, with the convergence of the COVID-19 pandemic and wildfires across the western United States,” said senior author Professor Francesca Dominici.

“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.”

Wildfires produce high levels of fine particle pollution, which has been linked to many adverse health conditions, such as asthma, chronic obstructive pulmonary diseases (COPD), and other respiratory illnesses. 

In 2020, massive wildfires struck the western United States, and the researchers looked at the subsequent PM2.5 air concentrations from monitoring data. The team developed a statistical model that also accounted for the number of COVID-19 cases and deaths in 92 counties that represented 95 percent of the population across California, Oregon, and Washington.



The study revealed that when fire activity was the highest – from August 15 to October 15, 2020 – daily levels of PM2.5 were an average of five times higher compared to days without wildfire activity. There were some instances when PM2.5 levels were extraordinarily high, reaching levels that are classified as “hazardous” by the U.S. Environmental Protection Agency.

According to the research, the effects of PM2.5 on COVID-19 cases were amplified for up to four weeks after individuals were exposed to the poor air quality.  

Ultimately, across all counties, a daily increase of 10 µg/m3 in PM2.5 each day for 28 subsequent days was associated with an 11.7 percent increase in COVID-19 cases, and an 8.4 percent increase in COVID-19 deaths. 

Some counties were hit much harder than others. In Whitman, Washington, higher PM2.5 levels were associated with a 71.6 percent increase in COVID-19 cases. Furthermore, San Bernardino, California had a 65.9 percent increase in fatal COVID-19 cases that were attributable to poor air quality from wildfire smoke. 

The experts report that across the three states studied, daily increases in PM2.5 from wildfires were linked to a total of 19,700 COVID-19 cases, and to an additional 750 fatal cases. 

“Climate change will likely bring warmer and drier conditions to the west, providing more fuel for fires to consume and further enhancing fire activity,” said Dominici.

“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.”

The study is published in the journal Science Advances.

By Chrissy Sexton, Staff Writer

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