The Harvard study looked at 92 counties in California, Oregon, and Washington impacted by wildfire in 2020. Using satellite images for the fires and public data on Covid-19 cases and deaths in the three Western states, researchers found that in the majority of the counties they studied, there was strong evidence that the more smoke and soot there was, the more there were cases and deaths from Covid. If PM 2.5 levels stayed higher for 28 days in a row, cases rose by nearly 12% and deaths by more than 8%.
"This is a very important study," Donghai Liang, professor of environmental health at Emory University, who was not involved in the study, told CNN. "This is among those first studies that really report the link between particulate matter coming out of the 2020 wildfires in the United States and how they contribute to the exacerbation on COVID-19 cases and deaths."
As the climate crisis accelerates, Liang said public health risks associated with wildfires may worsen. According to the landmark UN report published Monday, climate change-fueled drought and heat now make wildfire seasons longer and result in more destructive fires.
"Even without Covid, we've been concerned that climate change that leads to hotter environments, and droughts, is fodder for wildfires to occur," Rizzo said. "Then you add the wildfire ash and soot to the air quality, it does make respiratory issues much more likely to occur."
Tarik Benmarhnia, a climate change epidemiologist at Scripps Institution of Oceanography, told CNN the "repeat nature" of more frequent wildfires could exacerbate long-term public health impacts. Several studies have shown that short-term PM 2.5 exposure from wildfire smoke has led to increase in emergency department visits and hospitalizations.
"When you have a [wildfire] episode, we will see a huge increase in hospitalization for respiratory conditions or cardiovascular conditions -- and that's mostly the smoke, which is constituted mostly by PM 2.5," Benmarhnia said.
Certain communities are also at higher risk from exposure to wildfire smoke, including people with heart or lung disease, the elderly, the houseless, children, and babies. In a separate study published in April, Benmarhnia and his colleagues found that wildfire smoke is sending children ages 19 and younger to emergency rooms with respiratory problems at higher rates than ever before.
"Kids inhale way more air than us, and their respiratory system is still being developed," he said. "So they're way more vulnerable than adults and it could be a very dangerous situation."
It's not just the toxicity of wildfire smoke, but also what the fire burns. Once the fire reaches a community and chars houses, it burns materials such as plastic that contain hazardous chemicals. But unlike the smoke, Benmarhnia said, the toxic emissions are not transported as far away, making it a problem for local communities.
As wildfires intensify, Dominici says she hopes that the study will push more people to act on environmental justice for communities most impacted and also the climate crisis at large.
"I hope that by showing how catastrophic the combination of wildfires and Covid-19 is, this will be an additional piece of evidence for increasing the emergency of combating climate change," Dominici said.