The same team of Harvard researchers also published the first study to find a clear connection between long-term exposure to air pollution and Covid-19 death rates last year.
The new study included reported infections, not just deaths, which makes it especially interesting, said John Balmes, a professor of medicine at the University of California, San Francisco, and an expert on the health effects of pollution who was not involved in the research. “It’s one thing for air pollution to be increasing the severity of the coronavirus infection, it’s another for it to be increasing reported cases,” he said.
After decades of tightening air quality regulations, the air in many American cities is cleaner now than it’s been in 50 years. But in the West, increased wildfire smoke threatens to undo those advances, said Loretta Mickley, an atmospheric chemist at Harvard’s John A. Paulson School of Engineering and Applied Sciences and one of the paper’s authors.
As the planet warms, droughts intensify and the West becomes drier, wildfires are starting earlier, growing larger, spreading faster and reaching higher elevations. In California alone, a record 2.5 million acres burned during the 2020 wildfire season, 20 times what had burned the previous year.
“We are really talking about climate change,” said Francesca Dominici, a biostatistician at Harvard’s T.H. Chan School of Public Health and senior author of the paper. “I hope that this is providing an additional piece of evidence for why it’s important to get our act together to combat climate change.”
Wildfire smoke may contribute up to half of the PM 2.5 in some parts of the western United States. It is so far unclear whether wildfire smoke is more or less toxic than smoke from diesel combustion or power plants.
Dr. Dominici noted that the analysis did not include individual patient data or consider other factors such as mask mandates.
Researchers are currently investigating whether fine particulate matter can spread the coronavirus.
The research does not bode well for this year, Dr. Dominici said, as wildfires started early and the pandemic is still raging in the United States, with a Delta variant that tends to be more contagious. She added: “I think the wildfires will have the same, if not worse impact on Covid-19 cases and deaths among the unvaccinated.”