The Links Between Air Pollution and COVID-19

[This text was originally published in Catalan in EspaiS@lut newsletter of the Diputació de Barcelona.]

Ever since the start of the COVID-19 pandemic, people have speculated about whether there might be a link between air pollution and the spread of the virus. This was the subject of a study published in Environmental Health Perspectives. The findings suggested that higher levels of air pollution do not necessarily lead to increased risk of COVID-19 infection, but that in cases of long-term exposure to air pollution there is a greater risk of developing the disease among those who become infected with the virus. The study was co-led by ISGlobal and the Genomes for Life (GCAT) project at the Germans Trias i Pujol Research Institute (IGTP) in Badalona.

Prior to the publication of this research, various studies had already suggested that regions with higher pre-pandemic levels of air pollution had a higher incidence of COVID-19 cases and deaths during the first waves of the pandemic. However, the explanation for this association remains unclear; it could be that pollution increases airborne viral transmission, or that it increases a person’s susceptibility to becoming infected or ill with COVID-19. “The problem is that previous studies were based on confirmed—that is, diagnosed—cases, but missed all asymptomatic or undiagnosed cases,” explained ISGlobal researcher Manolis Kogevinas, lead author of the study.

Higher levels of air pollution do not necessarily lead to increased risk of COVID-19 infection, but that in cases of long-term exposure to air pollution there is a greater risk of developing the disease among those who become infected with the virus

The research team decided to combine technology developed by Dr. Carlota Dobaño’s team to measure a series of SARS-CoV-2 antibodies in a cohort of individuals living in Catalonia (COVICAT) with information on the residential exposure of these individuals to air pollutants (NO₂, PM_2.5, black carbon and ozone).

“This is the first study to perform mass screening for SARS-CoV-2 antibodies in a cohort of adults to study the association between long-term exposure to pre-pandemic air pollution, SARS-CoV-2 infection and disease,” commented Cathryn Tonne, who, together with Dobaño, was a senior co-author of the study. 

Increased Infectious Load and Symptom Severity

The study had a total of 9,605 participants, including 481 (5%) with confirmed cases of COVID-19. Blood samples were collected from just over 4,000 participants to measure levels of IgM, IgA and IgG antibodies against five viral antigens. Of those whose blood was tested, 18% had SARS-CoV-2 antibodies, but no association was found between infection and exposure to pollutants. However, for those who were seropositive—i.e. those who had been infected—an association was found between higher exposure to nitrogen dioxide (NO₂) and fine particulate matter (PM_2.5) and higher levels of IgG against all five viral antigens (indicating higher infectious load or symptom severity).

For the total population (all 9,605 participants), an association was found between higher exposure to NO₂ or PM_2.5 and illness (symptoms), especially for severe cases admitted to the hospital or intensive care unit. The association with PM_2.5 was strongest in men over 60 years of age and people living in more deprived areas.

Strongest Evidence to Date

“Our study provides the strongest evidence yet for the association between air pollution and COVID-19,” commented Kogevinas.

“The results are consistent with the association between pollution and hospitalisation that has been described for other respiratory infections such as influenza or pneumonia,” he added. Pollution can also aggravate chronic conditions, such as cardiovascular or respiratory disease, which increase the risk of becoming severely ill from COVID-19.

Pollution can also aggravate chronic conditions, such as cardiovascular or respiratory disease, which increase the risk of becoming severely ill from COVID-19

“The combination of the individual genetic risks previously identified in COVICAT participants and these new data on the environmental impact caused by exposure to air pollution will enhance our understanding of the complex interaction and mechanisms behind COVID-19 severity,” commented Rafael de Cid, a co-author from the IGTP.

The authors note that the findings provide additional support for the public health benefits of reducing levels of air pollution and underscore the impact of environmental factors on infectious diseases.