Study links wildfire smoke to rise in COVID-19 cases, deaths

Exposure to smoke intensifies risks for those who are infected, experts say

By Jeff Ballinger

Bay City News

A new study that links wildfire smoke with rising COVID-19 infections and deaths did not surprise local experts, who said the findings reinforce precautions taken by individuals and policymakers in the Bay Area and California.

The authors of a Harvard University study said they found evidence linking smoke from wildfires in California, Oregon and Washington in 2020 to rising COVID-19 cases and deaths. They said smoke carries with it fine particulate matter — or PM 2.5, known to have adverse effects on health — which acts as a vehicle for spreading infection even faster and making existing cases worse.

Local experts called it an important study that has implications not only for individual behavior but on climate change policy.

Dr. John Balmes warned of the potential link more than a year ago. He is a professor of medicine at University of California at San Francisco and, since 2008, has been the physician member of the California Air Resources Board.

In July 2020, Balmes told NPR there already was evidence suggesting people infected with COVID who are exposed to PM 2.5 have higher risk of severe infection and death.

“I was telling people last summer was that they should try to reduce exposure as much as possible,” he said in an interview.

In his capacity on CARB, Balmes recognizes the larger implications the study raises.

“If all of these wildfires don’t convince people that we have a climate emergency, I don’t know what will,” he said.

“We really need to double down on policies to get to clean transportation and get to clean energy,” he said. “We’re doing this in California, but we need the rest of the world to join us.”

The global implications also concern Dr. Mary Prunicki, director of air pollution and health research at the Sean N. Parker Center for Allergy and Asthma Research at Stanford University.

“The biggest takeaway is the ripple effect on climate change,” Prunicki said, calling it perhaps “the greatest health challenge of our time.”

Prunicki said the impact of wildfire smoke goes beyond COVID and will result in complications for everyone who breathes it.

“Wildfire smoke has lots of ways of impacting our health and increasing our susceptibility to COVID and any other type of infections,” she said.

Prunicki called the Harvard study an important one that highlights the need for everyone to take precautions, especially those who have, or have had, COVID.

“But any exposure to smoke will make you more susceptible,” she said. “Everybody needs to be worried about breathing the smoke.”

Balmes suggests several things people can do to protect themselves and reduce exposure to potentially toxic air, particularly when wildfires are in the area.

The first step is vaccination, which Balmes called “the best thing to control the pandemic.”

Then stay indoors when smoke is visible, or has been in the area recently, and wear a high-quality mask.

“If you have to go outside, wear an N95 mask,” Balmes said. “A cloth mask does nothing for wildfire smoke. A surgical mask maybe reduces the smoke by 20 percent.”

An N95 mask filters out PM 2.5, he said, and if those are unavailable, a KN95 mask is a second-best choice, although he warned that consumers need to be careful about counterfeit KN95 masks.

Because smoke can enter homes, even when windows are closed, using home filters can significantly reduce PM 2.5 when installed on home ventilation systems.

Balmes said homes without built-in systems don’t need expensive filtration systems. An inexpensive option can be homemade from a simple box fan with a HEPA or MERV-13 filter attached.

Directions for making one are available on the website of the Centers for Disease Control and Prevention, along with many other guidelines for precautions individuals can take, at

In addition, Prunicki urged people to work with their local schools to put correct measures in place.

The study, published in the journal Science Advances, can be found at

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