Study of Western Wildfires Links COVID-19 Cases to Smoke

A new study that links wildfire smoke with rising COVID-19 infections and deaths did not surprise local experts, who said the findings reinforce the precautions taken by individuals and policy makers 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 cases and deaths. They said that 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 was already evidence suggesting that 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 that they should try to reduce exposure as much as possible,” he said. In his capacity on the state board, Balmes recognized larger implications of the study.

“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.

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.

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

Balmes suggested 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 may reduce 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.

Since 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.

Prunicki added to the list Balmes suggests, urging people to work with their local schools to make sure they have the right measures in place.

The study was published in the journal Science Advances.

Jeff Ballinger is a reporter with Bay City News.



  1. COVID & Airborne Particulate? More reasons to Vote YES & END One-Party Mismanagement of CA.

    CA should be Fined for Spewing out record levels of “Green House Gases” across the country.
    Not to mention the adverse health effects due to the particulate matter residents get to breathe in – Increased Health Care Concerns & Costs.
    So Mis-Guided – Failure by Former Gov Brown and the Elitist disaster of Gov Gavin New(TAX)som.

    CA has neglected the safety & security of its Citizens while bowing to Special Interest Groups that file lawsuits to prevent proper management of timber in Forest Lands, Water resources and the environment.
    The amount of Climate Changing Pollutants released through CA’s environmental mismanagement resulting in increased frequency of larger Fires way outpaces any of the “trumpeted” gains through business stifling regulations on vehicle fuels, car manufacturers, energy producers, CEQA, etc..

    Another reason to RECALL Gavin Newsom and end the One Party Mis-Management of CA.

  2. “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.”

    Here we go again. Another “expert” making up a bunch of stuff they don’t know, can’t prove and no one can test and just telling us to believe them because they said so. This is even more absurd than wearing a surgical mask or cloth mask and thinking you’re somehow influencing the spread of a virus.

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