Air pollution: an underestimated negative prognostic factor for COVID-19

Air pollution is a driver of both COVID-19 morbidity and mortality. Different modes of action are discussed, including impairment of immune response, thus facilitating viral penetration and replication.

Even with air pollution levels decreasing during the lockdowns, the COVID-19 pandemic has highlighted adverse health impacts of air pollution. The best data exists for particulate matter (PM), nitrogen dioxide (NO₂), ozone (O₃), and sulphur dioxide (SO₂). The deposition of PM in the lungs can cause pulmonary injuries such as asthma, pulmonary dysfunction, pneumonia, and lung cancer. As Prof. Meredith McCormack (John Hopkins University, MD, USA) pointed out, the size of particles is directly linked to their potential for causing harm to the airways: particles that are smaller than 2.5 μm (PM2.5) can reach the terminal bronchioles and enter alveoli [1].

Air pollutants do not only impair the health of the respiratory system directly but can also increase the fatality of viral infections. In a Chinese study during the SARS epidemic, the fatality rate increased with the increment of the air pollution index [2]. This was also demonstrated in the COVID-19 pandemic [3]. Target organs of both COVID-19 and air pollution are the central nervous system, lungs, and heart. Different mechanisms can explain the detrimental effect of air pollution on a SARS-CoV-2 infection. Air pollutants impair the immune response, thus facilitating viral penetration and replication [3]. Furthermore, they exaggerate inflammatory and oxidative stress responses. Viruses may persist in air through complex interactions with particles and gases [3]. “In addition, PM and NO₂ exposures in vitro lead to overexpression of angiotensin-converting enzyme (ACE)2, a cellular target of SARS-CoV-2 that can lead to enhanced entry, infection, and replication,” Prof. McCormick said. There are estimates that particulate pollution from anthropogenic sources contributes to 15% of COVID-19 mortality worldwide [4].

According to another study, an increase of 1 µg/m³ in the long-term average PM2.5 is associated with an 11% increase in the COVID-19 mortality rate [5]. “We will see more studies like this. Moreover, air pollutants do not only influence mortality, but also morbidity,” Prof. McCormack said. Only recently the American Lung Association published the report ‘State of the air 2021’; according to this statement, even in the USA, more than 4 in 10 inhabitants live in places with unhealthy levels of air pollution [6]. “Air pollution does not affect all persons in the same way; poor people live in regions with higher air pollution. Accordingly, we have seen high death tolls of Latinos living in areas with higher air pollution,” Prof. McCormick explained.

Vice versa, cleaner air is a strategy to improve outcomes and reduce the impact of COVID-19. Maintaining and strengthening air quality standards is important to improve health around the globe. “Areas of improvement in air quality are opportunities to address health disparities.  COVID-19 provides a lens to reconsider air quality as a potential means to improve health,” concluded Prof. McCormack.

1. McCormack M, et al. Learning from our past and forging new frontiers in the COVID 19 era …air pollution exposure as a susceptibility factor for COVID 19 infection. Session A009: From dawn to dusk: pollutant exposures and susceptibility to respiratory infections. ATS 2021 International conference, 14-19 May 2021.
2. Cui Y, et al. Environ Health 2003;20:2:15.
3. Bourdrei Th, et al. Eur Respir Rev 2021;30(159):200242.
4. Pozzer A, et al. Cardiovasc Res 2020;116(14):2247-53.
5. Wu X, et al. Sci Adv 2020;6(45): eabd4049.
6. Report of the American Lung Association. Retrieved from https://www.lung.org/media/press-releases/sota-2021 on 18 May 2021.

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Posted on 5 July 2021