Wildfire Smoke Has Caused Rise in COVID Infections and Deaths, Study Finds

By Oliver Milman, Guardian UK

15 August 21

Researchers speculate that smoke helps spread the virus and weakens lungs, making symptoms more severe

ollutants in smoke billowing from huge wildfires in the west of America have probably caused an increase in Covid-19 infections and deaths across several US states, new research has found.

Last year more than 10m acres of land were torched by wildfires, with five out of the six largest fires ever documented in California occurring within just a few months. The burning trees, shrubs and buildings gave off enormous plumes of smoke containing small particles of soot.

The spread of these tiny particles, known as PM2.5, probably caused a spike in Covid cases and deaths in parts of the US west, the new paper has discovered. The smoke helped raise the coronavirus infection rate by nearly 20% in certain counties, with half of all Covid deaths in some places attributable to the pollution, according to the study.

“In some counties the association was very strong indeed – on days with lots of wildfire smoke the Covid cases went up by a lot,” said Francesca Dominici, a professor at the Harvard TH Chan School of Public Health who co-authored the research, which was led by Xiaodan Zhou, a researcher at Esri. “Combining wildfires with this pandemic can have a really disastrous effect. It’s disturbing.”

Previous research, which Dominici was also involved in, found that a small rise in people’s long-term exposure to air pollution is associated with an 11% increase in deaths from Covid. Another study from last year suggests that 15% of all Covid-19 deaths around the world are attributable to dirty air.

Researchers have said more work needs to be done to fully establish the connections but there was now compelling evidence that polluted air is exacerbating outbreaks of the coronavirus. It is thought that emitted pollutants can help spread the infection, while also weakening people’s lungs before they are infected with Covid, raising the likelihood they will get severely ill or die.

The latest paper, published in Science Advances, analyzed 92 counties across California, Washington and Oregon and sought to eliminate causes of Covid increases other than nearby wildfires. It found that the wildfires had the largest impact upon Covid cases in the counties of Butte, California, and Whitman, Washington. The greatest influence on Covid deaths, meanwhile, was found in Butte county and Calaveras county, California.

Last year’s spate of wildfires may well be surpassed in 2021, with huge blazes under way such as the Bootleg fire in Oregon, which at one point was the size of Los Angeles, and the Dixie fire in northern California, which is the largest in the state’s recorded history. The town of Greenville, California, was almost completely destroyed by fire last week.

Smoke from the fires has been detected from space, sweeping as far east as New York, where it turned the skies hazy. On Saturday, the city of Denver experienced the worst air quality in the world for several hours due to smoke from western wildfires.

“We only looked at counties in the west but I’d speculate that it doesn’t matter where you are, if you are getting high levels of PM2.5 from wildfire smoke in New York, you will get the same catastrophic effect,” said Dominici. “It’s very concerning. I’d say to anyone living in a place affected by wildfires to get vaccinated as soon as possible. Longer-term, this shows us, yet again, the importance of fighting climate change.”

Kristie Ebi, an epidemiologist at the University of Washington who was not involved in the research, said the study “adds to the weight of evidence that air pollution may increase sensitivity” to the coronavirus.

Ebi added that lockdowns and mask mandates were not fully factored into the paper, although the researchers did measure people’s mobility during the study period.

George Thurston, an expert in environmental medicine at New York University who also was not involved in the research, said: “The study findings are very plausible, in that tiny combustion particles are well known to pick up and carry other airborne toxins deep into the lung.”