Wildfire Smoke Linked to Covid-19 Cases and Deaths in the West

Thousands of coronavirus cases and hundreds of deaths may be attributable to the particulate matter in wildfire smoke

The Golden Gate Bridge and San Francisco skyline with a background of hazy, dark orange sky.
Smoke from nearby wildfires turned the sky above San Francisco a dark orange color last September. Christopher Michel via Flickr under CC BY 2.0

New research shows that smoke from last year’s unprecedented wildfire season in the western United States may have contributed to more than 19,000 Covid-19 cases and 700 deaths. The study, which is the first to quantify the link between small particulate matter from wildlife smoke and excess Covid-19 cases and deaths, was published Friday in Science Advances.

“The year 2020 brought unimaginable challenges in public health, with the convergence of the Covid-19 pandemic and wildfires across the western United States,” says study author Francesca Dominici to the Harvard Gazette’s Karen Feldscher.

Wildfire smoke contains tiny particulates called PM2.5, which are around one-fiftieth of the width of a human hair—small enough to get deep into lung tissue and cause widespread inflammation of the cells lining the airway and lungs. In addition to mouth, nose, and lung irritation, serious and prolonged exposure to PM2.5 can worsen asthma and heart disease, and make people more susceptible to viruses. The small particles can also trigger an immune response, reports Sarah Gibbens for National Geographic. In an effort to battle PM2.5, the immune system can’t put as much energy toward fighting Covid-19.

“The wildfires exacerbated the pandemic substantially,” says the study’s author Francesca Dominici to National Geographic, and inhaling the particulate in wildfire smoke is “compromising our ability to fight the virus.”

To assess the link between small particulate matter and Covid-19 cases, the Harvard University team of researchers gathered data from 92 counties in Washington, Oregon, and California between March and December 2020. They compared satellite data and EPA air quality assessments with publicly available health data to reveal that wildfire smoke was associated with an average increase of 11 percent more Covid-19 cases and 8 percent more deaths. In some counties in Washington and California, as many as 20 percent of Covid-19 cases were linked to PM2.5 exposure. According to their analysis, the particulate matter from the 2020 wildfire season contributed to a total of 19,742 Covid-19 cases and 748 deaths across the three states.

Last year was a recording-setting wildfire season in the West, and this year is already off to a historic start as California’s Dixie fire—the state’s second largest on record—is fueled by extreme drought and high winds. California’s previous fire season scorched over four million acres and releasing over 100 million tons of greenhouse gases and Washington saw more individual fires in 2020 than any other year on record.

Firefighting efforts have been complicated by limited access to personnel and resources throughout the global pandemic, and Dominici worries the emergence of more contagious Covid-19 variants during another historic wildfire season in the west may lead to more cases and deaths. For those trying to avoid harmful wildfire smoke and Covid-19, Dominici recommends wearing a mask that protects against both. But the single best way to protect yourself, she says, is getting fully vaccinated.

“Clearly, we see that, overall, this is a very dangerous combination,” says Dominici to Washington Post’s Joshua Partlow. “It’s a really scary thing as we continue to face these wildfires all around the world.”

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