Long-term air pollution may be a contributory factor in worsening the symptoms of COVID-19, concluded an expert committee, which recommended further research on the subject.
It is widely accepted that long-term exposure to air pollution contributes to the development and worsening of conditions such as cardiovascular and respiratory disease, which themselves have been shown to increase the risk of severe COVID-19 disease. "Exposure to high levels of air pollution can cause a range of health impacts," alerted Dr Malcolm White, clean air specialist at Global Action Plan, who told Medscape News UK that air pollution placed an "enormous burden" on the NHS.
Air pollution was the focus of the most recent annual report by England's chief medical officer, Professor Sir Chris Whitty, who highlighted how air pollution kills between 26,000 and 38,000 people each year in England. Aside from causing deaths, air pollution "causes quite a lot of disease and disability", alerted Professor Whitty, making it "everyone's problem".
Previous research has also found that exposure to outdoor and indoor air pollutants could put people at risk of other respiratory infections and worsen outcomes. Hence, it was proposed that air pollution may contribute to SARS-CoV-2 infection and COVID-19 severity.
Available Studies Limited and Inconsistent
The Committee on The Medical Effects of Air Pollutants (COMEAP) explained that since the start of the COVID pandemic in 2020, a large amount of research had been published linking air pollution and COVID-19 but "these studies have varied in quality and content".
For their new report, the Committee evaluated the current state of the science on the association between air pollution and COVID-19. "In the context of evidence for the effect of air pollution on lung infections more generally, long-term air pollution may be a contributory factor in worsening the symptoms of COVID-19," according to the authors.
However, the "limited" number of good quality studies, which were "often inconsistent" in their findings, led the Committee to conclude that based on available data up to the end of August 2022, there was not enough epidemiological evidence to suggest that long-term exposure to air pollution increased the risk of infection with the SARS-CoV-2 virus.
There was more evidence, underlined the authors, that long-term exposure to PM2.5 air pollution could increase the severity of COVID-19 disease once someone was infected with the virus, and that the risk of hospitalisation following infection was increased.
Although there was also some evidence for an increased risk of death from COVID-19, this evidence was "less clear" as few studies were available, the authors pointed out.
A small number of studies were available relating to possible mechanisms and these suggested ways air pollution could alter the body's immune function and, consequently, increase risk of COVID-19 infection. "We did not find convincing evidence to support air pollution particles having an important role in transporting viable SARS-CoV-2 virus in the environment," commented the authors, who emphasised that until more evidence became available, the Committee did not feel able to attempt to quantify the effects of air pollution on COVID-19 outcomes.
To date, there was "extremely limited" evidence on the influence that exposure to air pollution may have on recovery from SARS-CoV-2 infection, likewise with regards to whether air pollution exposure might affect the efficacy of COVID-19 vaccines or longer-term persistence of symptoms following infection.
More Research Required
Further research investigating long-term air pollution exposure with COVID-19 infection and adverse outcomes was required, particularly to help understand the influence that air pollution may have on susceptibility to and recovery from COVID-19, immune function, and the body's response to vaccination, stressed the authors. They recommended:
- Well-conducted cohort studies investigating whether prior long-term exposure to air pollution made individuals more susceptible to severe COVID-19 symptoms
- Experimental studies on the effects of air pollution exposure on the infectivity of the virus
- Research on the mechanisms by which air pollution alters immune function and increases susceptibility to respiratory infections
- Research assessing the impact of air pollution on the immune response to vaccination
- Investigation of the effects of lock-down and re-opening on air quality
The Committee acknowledged that studies linking air pollution and COVID-19 were difficult to conduct and "hard to interpret", and needed careful control for other factors that might influence exposure to the virus and disease severity. "Overall, we consider that the available studies on COVID-19, together with evidence of effects of air pollution on lower respiratory infections more generally, suggest that exposure to air pollution may worsen the symptoms of COVID-19 disease", concluded the authors.
Dr Charmaine Griffiths, chief executive of the British Heart Foundation, previously commented that more needed to be done to "make better air quality a reality". This sentiment was echoed by Cancer Research UK's chief executive, Michelle Mitchell, who alerted that air pollution was one of the "biggest environmental threats to health in the UK".
This article was updated on 11 September 2023 to include a comment by Dr Malcolm White