COVID-19—the disease caused by the novel coronavirus—mainly affects a person’s lungs. Researchers know that patients with pre-existing respiratory and heart conditions are at a higher risk for developing severe—and potentially deadly—cases of COVID-19, according to the Centers for Disease Control and Prevention. Scientists are racing to learn as much as possible about this new disease, its complications and what communities may be at more risk than others.
Because complications associated with lung and heart health issues are already linked to air pollution, scientists have started investigating whether people living in areas with poor air quality may also be more susceptible to severe cases of COVID-19. Preliminary findings in the United States, England, Northern Italy and China have all found that cities with high rates of air pollution are also facing higher COVID-19 death rates.
“We don’t have the evidence linking directly to mortality yet, but we know if you are exposed to air pollution you are increasing your chances of being more severely affected,” María Neira, director of public health at the World Health Organization (WHO), tells Damian Carrington at the Guardian. “We are starting to give messages to countries and regions saying, if you are starting to have cases, in those cities where you have a high level of pollution, reinforce your level of preparedness, because you might have a higher mortality.”
Tiny air pollution particles—known to researchers as PM2.5, which stands for particulate matter smaller than 2.5 micrometers—are associated with burning certain material, including coal and gasoline. Inhaling PM2.5 for many years can lead to increased risk of heart attacks, premature death in people with heart or lung disease, worsened asthma symptoms, decreased lung function, and airway irritation that can lead to coughing or difficulty breathing, according to the Environmental Protection Agency.
One of the preliminary studies linking air pollution to an increased COVID-19 death rate covered “more than 3,000 counties in the United States (representing 98 percent of the population)” and found that even a “small increase in long-term exposure to PM2.5 leads to a large increase in the COVID-19 death rate,” the team researchers from Harvard University writes in the paper.
To determine whether air pollution is significantly linked COVID-19 mortality rates, the Harvard researchers took 20 additional factors into account, including “population size, age distribution, population density, time since the beginning of the outbreak, time since state’s issuance of stay-at-home order, hospital beds, number of individuals tested, weather, and socioeconomic and behavioral variables such as obesity and smoking,” according to the study.
The study found long term exposure to just one additional microgram per cubic meter of PM2.5 was associated with an eight percent increase in the COVID-19 death rate in a given city. (An earlier version of the study reported a 15 percent increase in mortality but the updated figure reflects the addition of data up to April 22. The team plans to update their analyses routinely.)
“If you’re getting COVID, and you have been breathing polluted air, it’s really putting gasoline on a fire,” Francesca Dominici, a Harvard biostatistics professor and the study’s senior author, told Beth Gardiner at National Geographic in early April.
Researchers are still unsure why air pollution is linked to increased COVID-19 mortality. But as Ula Chobrok reports for Popular Science, one team hypothesizes that the immune system may respond in similar ways to both threats.
According to the study published in the journal Environmental Pollution, COVID-19 and air pollution both trigger cytokine-related inflammation, during which the immune system releases cytokine molecules to fight off the threat in the lungs. But this reaction can occasionally cause a buildup of fluid or a “cytokine storm” that can attack healthy tissue, thus weakening the body’s defense against other threats, including COVID-19, as outlined in Popular Science.
“The importance of the paper is the correlation we found from the actions of pollution in the immune system and the actions of the virus,” Caro tells Popular Science. “Because inflammation of cytokines is the first step to die from coronavirus, we can say that this step for people living in a polluted area is already done.”
A similar link to high mortality rates in cities with polluted air was established during 2003 SARS outbreak, another respiratory infection caused by a coronavirus. The 2003 study’s author Zuo-Feng Zhang, the associate dean for research at the University of California, Los Angeles, tells Lisa Friedman of the New York Times that Harvard’s COVID-19 study is “very much consistent” with his prior findings.
Ironically, the COVID-19 lockdowns and shelter-in-place orders means fewer people are driving or flying, which has led to clearer skies. In India, the famously polluted New Delhi saw a 60 percent drop in PM2.5 levels from March 23 to April 13 in 2020 compared to figures from 2019, reports Helen Regan for CNN.
In the U.S., Los Angeles enjoyed more than 18 days of clean air in March—the city’s longest recorded stretch of clear days—along with a 31 percent reduction of PM 2.5 compared to 2019 and a 51 percent reduction from the average over the prior four years, reports CNN.
These short-term decreases in air pollution can’t reverse long-term respiratory conditions, but research suggests that even short periods of clean air can ease symptoms of airway irritation. Marshall Burke, an Earth system scientist at Stanford University, calculated that tens of thousands of lives were saved in China due to cleaner air, according to National Geographic. Burke emphasizes that his estimate should not be seen as a comment on the pandemic itself, but rather a window into how the skies could be improved if society takes the appropriate measures.
“[T]hese other things we do, that we can change, are also important,” he tells National Geographic. “Lives we lose absent a pandemic are also really important, and are lives we shouldn’t lose.”