Wildfire smoke had choked the mountain valleys of western Montana for nearly two months when a team of university researchers landed in Seeley Lake in the fall of 2017. Students and faculty left  their labs behind, headed to the small community and launched a study on how the relentless wildfire smoke was affecting the health of the people breathing it.

The results of their study, published in the journal Toxics this summer, were stunning. They showed that lung function in the 100 Montanans who participated declined the year after the fires and stayed compromised the year after that, said lead researcher, Christopher T. Migliaccio, whose work at the University of Montana focuses on how environmental factors affect respiratory function and immunity, with an emphasis on wildfire smoke exposures.

“Seeing that there is this long-term effect is new,” he said, in telling how the findings showed that short-term symptoms like scratchy throats and persistent coughing were only part of the story. 

In a year when wildfires have burned 8 million acres across America, findings like these have raised concern to new levels—not only because Colorado and California both suffered through their largest fires in history this year, but also because of the global pandemic. 

Worry is only growing as the fire season expands into the flu season, and continues to choke the air with wildfire smoke, while the risk of Covid-19 infections swells, too. Roughly 78 million people who live in the smoky West also face heightened health risks from two viruses, the common flu and the strange and unchecked coronavirus that has claimed more than 223,000 American lives in a matter of months.

Concern about the health risks from wildfire smoke is growing 

More than a dozen studies have emerged from around the world in recent weeks on how air pollution affects Covid-19, but many urgent questions remain. Will I get sicker from the coronavirus because I inhaled so much wildfire smoke for so long? Am I more likely to die from Covid-19 because I live downwind of these massive wildfires? As a coronavirus survivor, am I more vulnerable to wildfire smoke? Does wood smoke harm my health even more than urban pollution?

“When it comes to how we might expect wildfire smoke to exacerbate Covid-19 risks, we don’t know yet, since we are just now experiencing our 2020 wildfire season with this new emerging infectious disease,” said Erin Landguth, an associate professor in the Center for Population Health Research at the University of Montana. “However, we have a lot of pieces to this puzzle that warrant concern.”

Solid answers about the connection between air pollution and Covid-19 are probably two years away, said C. Arden Pope, a researcher at Brigham Young University who pioneered air pollution epidemiology.

But, he added, “It would not surprise me if air pollution contributes to the risk of coronavirus infection.”

Pope’s own research, reported two years ago in the American Journal of Respiratory Critical Care Medicine, has linked PM2.5 air pollution—particulate matter that is smaller than 2.5 microns, or about 30 times smaller than a human hair—to the influenza virus.

And even though that link has been well established in research, the most prominent study so far linking air pollution with the coronavirus has taken heat, Pope noted. The T.H. Chan School of Public Health at Harvard University last spring projected an 8 percent increase in mortality for increased pollution concentrations as small as 1 microgram of PM2.5 per cubic meter of air.

Since then, other studies have linked higher air pollution exposures to increased severity of Covid-19 infections. But so far, no research specifically ties wildfire smoke exposure to increased infection from the coronavirus or severity of symptoms, scientists told InsideClimate News.

Air pollution, regardless of its source, harms health

How PM 2.5 makes people sick has been the subject of thousands of studies over decades. These microscopic particles of soot, which come from fossil fuel combustion as well as from burning forests and grasslands, burrow into the sensitive lining of the lungs, triggering heart and lung damage. They also are sometimes small enough to pass into the bloodstream.

The World Health Organization blames indoor pollution from burning wood and other fuels used for cooking and heating for 4 million premature deaths a year—just as many as from outdoor pollution sources.

Landguth pointed out that groups considered “sensitive” to air pollution make up about 30 percent of the U.S. population. Children under 18, adults over 65, women who are pregnant and those with medical conditions such as heart or lung disease, COPD, asthma, diabetes or compromised immune systems are included in that group. So are those who work outdoors or who have lower socioeconomic status, such as people who are homeless and those with limited access to medical care.

A subset of studies has begun drilling down into the health impacts of pollution from wildfires. One was led by Landguth, who reviewed a decade’s worth of data on PM 2.5 from wildfires in Montana and hospitalizations and urgent-care clinic visits for influenza. 

Past studies of wildfire smoke have focused on acute cardiopulmonary health effects that happen within days or weeks of exposure. Landguth said that’s the timeframe the researchers expected to see increased treatment for flu in this study. Her team, however, was shocked to find delayed effects, as well.

After bad summer fire seasons, influenza was three to five times worse during the traditional flu season of fall and winter. After four bad fire years, including 2017, the number of annual flu cases in Montana jumped from the typical 3,000 to around 12,000. 

“We were just—we couldn’t believe it,” she said, noting that the lag time was months, rather than days or weeks.

“We’re furiously pulling in that data right now trying to see if this association is gonna hold across other states [because] wildfire season is a lot longer in California, and it’s different in Oregon and Washington and Colorado,” she said. “We don’t know. We need to investigate that.”

Even though there hasn’t been enough time to compile the peer-reviewed research that doctors and public health professionals rely on, the coronavirus-wildfire smoke connections are already seen as significant. The federal Centers for Disease Control and Prevention updated its coronavirus website this summer to say that people with Covid-19 are at increased risk from wildfire smoke, Landguth pointed out.

“Wildfire smoke can irritate your lungs, cause inflammation, affect your immune system and make you more prone to lung infections, including SARS-CoV-2, the virus that causes COVID-19,” the CDC page says. “Know how wildfire smoke can affect you and your loved ones during the COVID-19 pandemic and what you can do to protect yourselves.”

The size and duration of this summer’s western wildfires have prompted a growing urgency to find answers to questions about the smoke-pandemic dynamic. But researchers mention longer-term concerns too.

Climate change is increasing the likelihood of wildfire, and the health burden of fire pollution on public health is growing, too. And the addition of the coronavirus to the mix adds still more concern.

A study published this week in Nature Sustainability underscores the scope of the potential impacts from the converging trends. In it, researchers detailed how the health care costs associated with PM 2.5 from the 2019-20 Australian megafires was nearly $1.4 billion (in U.S. dollars), with 3,230 hospital admissions for cardiovascular and respiratory disorders and 429 premature deaths attributed to the smoke.

Scientist Marshall Burke, associate professor in Stanford University’s Department of Earth System Science, is researching the overall health costs of exposure to six weeks of smoke from the recent wildfires across the West Coast. Early findings suggest that the smoke impacts are huge, possibly responsible for serious disease or death in thousands of people.

“It’s really important in thinking about the overall cost,” he said, “putting a sort of a back of the envelope magnitude, on how large these hidden costs could be.”.

Burke said he needs to see more data before he would conclude that a bad fire year will cause more severe illness and more frequent death from Covid-19. Studies only suggest “the plausible biological story that exposure to air pollution worsens immune function,” he said.

“We’ve seen that it causes you to either be more susceptible to viral infection or more harmed by it if you are exposed or infected,” he said. But “there has not been the smoking gun study that totally proves that true.”

Many experts on air pollution and health have been fielding questions about Covid-19 and the wildfire smoke all summer. It’s hard to find the right answer, said Colleen E. Reid, an assistant professor in the department of geography at the University of Colorado in Boulder, who has literally been in the thick of it, as hundreds of thousands of acres burn in her state.

“The recommendations we have for protecting health need to be studied more to know what’s really effective,” she said, noting that most recommendations are based on common sense and good judgment. 

Some are asking how to tell if their cough is from Covid-19 or from breathing wildfire smoke for days. People who live in poorly insulated or leaky homes might seek relief from the heat and smoke at a mall or public library with better ventilation, but that could increase the risk of being exposed to the coronavirus. 

“We need more evidence,” she said, “about the efficacy of different specific interventions that could protect people from smoke.”

Migliaccio, the University of Montana researcher, has also been fielding calls about managing personal risk as coronavirus case rates climb in his state and the flu season picks up. Some of those calls are from the 109 people who participated in the Seeley Lake study two years ago.

The pandemic prevented researchers from doing followup spirometry tests this summer, he said, so his team hasn’t been able to measure how much those research subjects have healed from the smoke of 2017. Migliaccio said he talks to them about the importance of taking precautions against the flu, such as getting the annual vaccine, as well as the masks and social distancing credited with the spread of Covid-19.

“Be even more vigilant” about taking steps against the twin viruses, he said he tells them, “because you’re going to be a little bit compromised, unfortunately.”