President Biden, in his January 27, 2021 speech on combating climate change, stated “Multiple studies have shown that air pollution is associated with an increased risk of death from COVID-19.” The president presented his climate change plan as a course of action that will not only reduce global warming, but also create jobs and clean up the air. While we all hope the COVID-19 pandemic will be over before President Biden’s climate change plan has an impact, COVID-19 wasn’t the first respiratory viral pandemic and it is unlikely to be the last. By reducing air pollution, we can save both current and future lives.
Air pollution increases the incidence of respiratory and cardiovascular comorbidities (Brook et al., 2010; Kelly and Fussell, 2015; Thurston et al., 2017) that increase the risk of hospitalization and/or death from COVID. Before a single study was performed on COVID and air pollution, we had every reason to believe that air pollution would be a factor affecting SARS-CoV-2 infection.
For five days in 1952, the Great Smog of London ended the life of an estimated 12,000 people, in many cases from pneumonia. Research has demonstrated a causal link between air pollution and an increased susceptibility to respiratory infections (Domingo and Rovira, 2020; Thurston et al., 2017; Woodby et al. 2020).
Air pollution causes chronic inflammation which impacts our ability to fight the virus. Ongoing research is delineating the mechanisms by which air pollution impairs the ability of the lungs to fight off infection, focusing on the specific effects of air pollution on various components of our immune system (Woodby et al, 2020).
Early on in the pandemic, reports showed that areas of Italy, China, and the US with high levels of air pollution also had a high incidence of COVID and high hospital admissions due to COVID (Fattorini et al, 2020; Frontera et al., 2020; Zhu et al, 2020; Wu et al., 2020). A more recent report has taken into account population density and the age distribution of the populations, and still, the association of COVID with air pollution remains (Fisca et al, 2020).
The strongest evidence for a specific link between COVID and air pollution will be found when data on individuals, not just population-wide data, are obtained. Individual data will allow other risk factors such as preexisting conditions, age, smoking, and gender to be adjusted for. Unfortunately, these types of studies take time.
One of the widely accepted guidelines for assessing causality is that there be a plausible mechanism by which a condition could cause a disorder. In the case of air pollution and COVID, there are many possible mechanisms that are currently being explored, and it is likely that we will find that air pollution increases COVID morbidity and mortality by a combination of ways (Wang et al., 2020; Woodby et al, 2020 ).
One of these hypothesized mechanisms concerns the ACE-2 receptor (Borro et al, 2020). All viruses consist of either DNA or RNA (but not both) and protein, and some viruses like SARS-CoV-2, are enclosed by an outer envelope. Unlike bacteria, viruses are not cells and must rely on a host cell to reproduce. In order for the SARS-CoV-2 virus to enter the host cell, its S protein must first bind with the ACE-2 receptor (a protein) embedded in the cell membrane. Cell membranes control what enters and leaves the cell. Air pollution has been shown to increase synthesis of ACE-2 receptors (Lin et al., 2018). Therefore, air pollution causes more proteins to be produced that would usher the virus into our cells, potentially increasing the likelihood of infection.
We all had a glimpse of what the world would be like with less pollution when traffic and industry took a brief hiatus last spring. The clear air allowed us to see beautiful vistas in India and Los Angeles long covered up by polluted air. We need to support every effort our president and government make to clean up our air, so as to reduce climate change, create jobs, improve our health, and last but not least, to lessen the impact of the next pandemic.
References
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