Air Pollution Increases COVID

Exposure to air pollution increases the risk of contracting COVID-19 and results in more severe disease, according to two new studies comparing medical outcomes and pollution levels in Belgium and Denmark, published in the European Respiratory Journal.

Scientists found that COVID-19 patients who had lived with poor air quality spent days longer in the hospital, were more likely to need intensive care, and faced a greater chance of dying from the disease. The finding signals ways governments can reduce deaths from not only COVID-19 but also other respiratory illnesses and future pandemics.

In the Danish study, researchers collected data from the Danish National COVID-19 Surveillance System on the 3.7 million people older than 30 living in the country during the first 14 months of the pandemic. These data were combined with the pollution levels at people’s home addresses for the previous 20 years.

In addition to pollution data, the researchers had access to comprehensive data for testing, hospitalization, and death, thanks to a centralized collection system. “We could follow the entire population of the country,” said environmental epidemiologist Zorana Jovanovic Andersen from the University of Copenhagen, Denmark.

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“We knew even before COVID that air pollution does something to our immune systems and makes us more vulnerable to infections like pneumonia.”

Andersen and her colleagues found that increased long-term exposure to nitrogen dioxide and fine particulate matter, even at levels within the European Union’s current legal standards, increased the risk of contracting COVID-19 by more than 10% and of being hospitalized by more than 9%. People exposed to higher levels of air pollution had a 23% greater chance of dying from the disease, the researchers found.

Those from less affluent backgrounds or with certain chronic illnesses, such as heart disease and asthma, were most vulnerable to the combined effects of air pollution and COVID-19.

“We are sure that we see an association,” Andersen said. “We knew even before COVID that air pollution does something to our immune systems and makes us more vulnerable to infections like pneumonia.”

In the study out of Belgium, researchers focused on 328 patients who were hospitalized for COVID-19 between May 2020 and March 2021. By comparing the pollution levels at the patient’s home addresses with their medical outcomes, the researchers found that those with higher exposure to air pollution in the week before being hospitalized stayed an average of four more days in the hospital. High exposure to nitrogen dioxide more than doubled the risk of intensive care unit (ICU) admission.

Having exposure to air pollution was equivalent to being a decade older, according to the authors of the study in Belgium. At the same time, reduced exposure decreased patients’ hospitalization time by 40%–80%—as much as some of the best available treatments.

“To put it very simply, a 40-year-old with high air pollution [exposure] and a 50-year-old with low air pollution [exposure] are at about the same risk.”

“To put it very simply, a 40-year-old with high air pollution [exposure] and a 50-year-old with low air pollution [exposure] are at about the same risk,” said environmental epidemiologist Tim Nawrot from Hasselt University in Belgium.

In both studies, the researchers determined the pollution levels people were exposed to by using chemical transport models—computer simulations that combine meteorological data, satellite observations, pollution levels measured at sampling stations on the ground, topography, and other factors.

The Belgian researchers also took blood samples from the patients to measure the levels of black carbon—soot remnant of the incomplete combustion of fossil fuels and biomass. Like nitrogen dioxide, black carbon is often linked to vehicle engine exhaust and wood burning.

Patients with higher soot levels in their blood were 36% more likely to need intensive care.

The findings were expected, Nawrot said. Even before the COVID-19 pandemic, researchers had seen that patients exposed to higher levels of pollution the weeks before admission required longer ventilation time in the ICU, independent of the cause of hospitalization.

“It was surprising to see the magnitude of the effect even though it is a small exposure,” said doctoral student Stijn Vos from Hasselt University, the lead author of the Belgian study.

“We have now quite clear consistent evidence of the relationship between air pollution and COVID severity,” said Cathryn Tonne, an environmental epidemiologist at the Barcelona Institute for Global Health in Spain who wasn’t involved with either study. Tonne’s research showed similar results in Catalonia, a region in northeastern Spain with a population about the size of Denmark’s.

Although earlier studies showed a link between COVID-19 and air pollution, they were what epidemiologists call “ecological studies,” which use averaged data for whole populations. They can provide an early assessment but are subject to many problems and factors that cannot be controlled. The new studies consider the situation of each patient, looking at factors such as occupation, educational level, income, and number of people in the same household to avoid bias introduced by these factors.

Universal health care policies afforded the researchers detailed data. “You can’t do this in the [United States]; you can’t do this in many other places where you don’t have universal health care or it’s a much more fragmented system,” Tonne said.

Air pollution is the fourth greatest health risk factor, after smoking, high blood pressure, and diet. It causes more than 6 million deaths every year. Airborne particulates and toxins are responsible for many diseases, but as a risk factor, exposure to them affects everyone, not only those with poor health habits.

For that reason, small reductions in air pollution bring significant public health benefits, Andersen said. Policies regarding air quality could be seen as public health measures. “That’s why we don’t need to stress people over it, but we need to stress our governments,” Andersen said.

The new studies show that lowering air pollution is an important part of pandemic preparedness, Tonne said. “If we have high levels of air pollution, you’re going to have a much worse time when the next pandemic comes,” she added.

—Javier Barbuzano (@javibarbuzano), Science Writer