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Poor Air Quality From Wildfire Smoke Worsens COVID-19 Cases, Deaths, Study Finds

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A view of the San Francisco skyline from Dolores Park in San Francisco on Sept. 9, 2020. (Beth LaBerge/KQED)

On Sept. 9, 2020, the Bay Area sky turned so hazy, it hid the sun from view and glowed an ominous dark orange. In the days that followed, dangerous air pollution in the region skyrocketed as dozens of wildfires burned throughout California, in what became the largest wildfire season recorded in modern state history.

But like other essential workers, Maribel Villanueva, 46, kept working, caring for children full-time at a day care in East Oakland. She walked and took a 20-minute bus ride to work wearing a cloth mask, which didn’t protect her from the worst of the smoke, said Maribel’s sister, Susana. She developed a loud cough, and on Sept. 17, Maribel was hospitalized with COVID-19.

“Before we even knew that she had COVID, she had cold-like symptoms and said, ‘You know, I think it was the smoke that really affected me. And that's why I have this cough,’” said Susana, 42, who lived with Maribel and other relatives in their home in Oakland.

Susana will never know for certain the extent of the smoke’s harm to her sister’s lungs. But two weeks later, on Oct. 2, Maribel died at a hospital from respiratory failure, pneumonia and COVID-19, according to her death certificate. A single mom, she left behind a son who just turned 11 years old.

The two natural disasters — the coronavirus and record-setting Western wildfires spewing air toxins — converged to exacerbate the pandemic’s health toll last year in California, Oregon and Washington, according to a study published Friday in the journal Science Advances.


Wildfire smoke produces high levels of tiny, harmful particulate matter, so-called PM 2.5, that can travel suspended in air thousands of miles away.

More wildfire coverage

In California alone, between mid-March and mid-December 2020, exposure to high levels of PM 2.5 contributed to about 1,000 COVID-19 deaths and 26,600 cases in counties where the smoke was found to amplify coronavirus cases or mortality. The researchers of the study, from Harvard University and other institutions, provided KQED with county numbers in advance of publication.

Alameda County, where Maribel Villanueva lived, faced one of the biggest spikes in COVID-19 deaths linked to wildfire smoke pollution out of the 92 counties the researchers analyzed.

Smoke increases risk of lung infections

Inhaling wildfire smoke can cause inflammation in the lungs and hurt the immune system’s response, making people more prone to severe respiratory tract infections, including from COVID-19, according to medical experts and the Centers for Disease Control and Prevention.

“It made perfect sense to me that the bad wildfire smoke season we had in 2020 here in Northern California would lead to increased risk of COVID-19,” said John Balmes, a pulmonologist at UCSF who reviewed the study for KQED.

Susana Villanueva holds a photo of her sister Maribel at her home in Oakland on Aug. 3, 2021. Maribel, a day care worker and single mom, developed a cough after inhaling wildfire smoke in Sept. 2020. She died weeks later from COVID-19. (Farida Jhabvala Romero/KQED)

Previous research has linked air pollution to worse COVID-19 health outcomes, including a recent study that found that higher PM 2.5 from wildfire smoke led to 18% more COVID-19 cases in Reno, Nevada.

But this is the first investigation that quantifies the extra number of coronavirus cases and deaths due to wildfire pollution in multiple states, said senior author Francesca Dominici, a professor of biostatistics at the Harvard T.H. Chan School of Public Health.

Dominici said the study makes a clear link between climate change and the pandemic. Climate experts have established that the warming climate is a major driver of drought and heat conditions that lead to more frequent and catastrophic blazes.

“We now know that these wildfires, because of their very high levels of PM 2.5, are making the pandemic worse,” said Dominici. “Wildfire [smoke] exposure and COVID are actually a really dangerous combination.”

Dominici’s research team developed a statistical model that crunched county-level data on the coronavirus, smoke and PM 2.5 to estimate excess COVID-19 cases and deaths up to four weeks after a day of extra air pollution due to the blazes.

While wildfire smoke exacerbated the coronavirus health burden in most counties, the smoke seemed to have a “protective effect” leading to fewer coronavirus cases or deaths in others, including Los Angeles and San Mateo. That’s because there are many other factors at play, such as adherence to mask mandates, said Dominici.

“It's entirely possible that during wildfire days people stayed indoors more, and this contained ... the spread of the disease,” she said. “And so people were actually exposed less to the levels of PM 2.5 during these days.”

‘Like he was drowning’

Adrian Sanchez, 72, lived in South Hayward, in a lower-income ZIP code that has suffered one of the highest rates of COVID-19 deaths in Alameda County.

The former forklift operator died from the coronavirus on Dec. 5, and lived with both Type 2 diabetes and asthma — two conditions that make COVID-19 and smoke more dangerous.

His wife of 46 years, Eudelia, remembers Adrian struggling to breathe on heavy smoke days last summer and fall. He felt “like he was drowning” because of his asthma, she said in Spanish.

“It’s going to be very difficult for us to recover. The pain is always going to be there,” said Eudelia, 68, who believes the smoke pollution harmed her husband’s health.

“Obviously, if the smoke impacts people who are healthy, can you imagine what it does to those who are already sick?” she asked.

During the worst of last year’s wildfire season, between mid-August and mid-October, 162 people in Alameda County died from the coronavirus, according to an analysis of county records by the Documenting COVID-19 project from the Brown Institute for Media Innovation, a collaboration between Columbia and Stanford universities, in collaboration with KQED.

County medical examiner data, which includes the occupation of those who died, shows that nearly all of the deceased under age 65 were in frontline jobs, including janitors, delivery drivers, caregivers and construction workers.

Susana Villanueva at home in Oakland with Maribel's son David Lara, 11. After Maribel's death last fall, Susana and her husband took custody of David. (Beth LaBerge/KQED)

Air pollution as environmental justice issue

To protect themselves, people should avoid smoke as much as possible and wear N95 masks when they venture outdoors.

Inside buildings, using central air conditioning or air cleaners cuts down particulate matter, said Amy MacPherson, a spokesperson with the California Air Resources Board, or CARB, which is tasked with protecting the public from air pollution.

“The single most effective way to protect yourself from wildfire smoke is to stay indoors, with windows and doors shut,” said MacPherson.

But avoiding smoke is often unrealistic for millions of people who work outside the home and toil outdoors in industries such as construction or agriculture, or who rely on public transportation.

These workers often live in lower-income communities of color, in older homes that lack air purifiers and that smoke can easily penetrate, said Balmes, the UCSF physician who has researched the impacts of air pollution on lung health for nearly 40 years.

He added that those same communities, with less access to medical care or healthy foods, also suffer disproportionately from chronic conditions such as heart disease and diabetes that can worsen COVID-19 symptoms.

“Exposure to air pollution in general and wildfire smoke in particular, tends to be greater for low-income people of color, but then they're also at greater risk for COVID-19,” said Balmes. “So it's an environmental justice issue that our society should be dealing with.”

Local governments should do more to provide free N95 masks and portable air filters to lower-wage families, especially essential workers, said Balmes, who was first appointed as a member of CARB by Gov. Arnold Schwarzenegger.

The agency is planning to provide $5 million in the next few months to local communities to upgrade ventilation systems and purchase portable air cleaners. The goal is to set up a “network of clean air centers” to help vulnerable populations get relief from the smoke, said CARB spokesperson MacPherson.

Last week, the Bay Area Air Quality Management District announced it will offer portable air filtration units to about 2,000 lower-income residents diagnosed with asthma, and who are particularly at risk from the pollution expected this wildfire season.

And a bill introduced last month by California and Oregon senators would allow the president to declare a “smoke emergency” and direct funds, equipment, personnel and other resources to set up smoke shelters, air purifiers and air monitors in affected communities.

Families of both Adrian Sanchez and Maribel Villanueva, the day care worker, said they didn’t have an air purifier at home or N95 masks to wear when they went outdoors.

After Maribel’s funeral, her sister Susana took custody of Maribel’s young son. The family gathered during his 11th birthday celebration at Susana’s home. But as he stared at his red velvet cake, the boy looked like he was going to cry, missing his mom, said Susana.

“I tell him, ‘I will never be able to replace your mom, but I'm here. We love you. I want you to know that we care for you,”' she said. “So just taking it one day at a time.”

Jake Kincaid and Derek Kravitz of the Documenting COVID-19 project contributed data analysis on COVID-19 deaths in Alameda County during wildfire season for this report.

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