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• Posted June 18, 2025

How Wildfires Might Increase Risk Of Flu, COVID-19

WEDNESDAY, June 18, 2025 (HealthDay News) — Wildfires might inadvertently increase the risk of flu and COVID-19 outbreaks, a new study argues.

Sky-choking wildfire smoke tends to drive people indoors, and infectious diseases are more likely to spread among those packed into enclosed spaces, researchers reported today in the journal PLOS Climate.

“Our findings show that wildfires led to a dramatic increase in indoor activities, creating the ideal conditions for respiratory diseases such as influenza to spread,” wrote the research team led by senior researcher Giulia Pullano, a postdoctoral fellow in epidemiology at Georgetown University in Washington, D.C.

“But by incorporating simple measures like indoor mask-wearing, we can reduce this risk,” the team added.

For the study, researchers analyzed mobile phone data tracking people’s visits to more than 4.6 million points of interest throughout the United States, including both indoor and outdoor destinations.

The team then zeroed in on the wildfire season that disrupted activities in Oregon and Washington between July and November 2020, using air quality data to identify counties worst affected by wildfire smoke.

In August 2020, thunderstorms sparked multiple wildfires in those states, researchers said in background notes. A windy, record-breaking heatwave added fuel to the fires in September, spreading smoke across Oregon and Washington.

Results show that during the wildfires, counties in Oregon experienced a 14% increase in indoor activity and Washington counties a nearly 11% increase.

Major cities in those states also experienced a surge in indoor activities – 16% in Seattle and 11% in Portland.

Computer models show packing that many extra people indoors will increase the risk of infectious disease spread, particularly for virulent airborne diseases like influenza and COVID-19, researchers said.

However, the models also showed that wearing masks indoors can limit transmission.

“We find that even a modest increase in mask use (10%) can reduce the rise in peak incidence during wildfires,” researchers wrote. “In heavily impacted areas like Washington County, Ore., and Yakima County, Wash., masking rates above 50% may be required to effectively mitigate disease transmission.”

Public health experts should keep this effect in mind if wildfire smoke drifts into their region, and warn people of the increased infection risk, researchers explained.

“As we face more frequent extreme events, public health strategies must evolve to address not just the environmental impact, but also the ways we adapt and react to the emergency,” researchers wrote.

“By understanding and planning for this behavioral response, we can better protect public health in a warming world,” they concluded.

More information

The U.S. Centers for Disease Control and Prevention has more on how wildfire smoke affects health.

SOURCES: PLOS Climate, journal; PLOS, news release, June 18, 2025