Investigating the links between air pollution, COVID-19 and lower respiratory infectious diseases

The Greater London Authority commissioned researchers from the Environment Research Group (ERG) at Imperial College London to investigate the links between air pollution, COVID-19 and other infectious diseases in London.

Air pollution has harmful effects on the lungs. When COVID-19, a disease which infects the airways of the lungs, became a global pandemic it raised the question - does air pollution increase the chance of catching COVID-19 or worsen health outcomes if you do contract it?

In a remarkably short time hundreds of papers have been published about COVID-19 and air pollution. These papers have varied widely in quality and content. A review of studies until November 2020 concluded that there were emerging findings on air pollution and COVID-19 but, in the type of studies done at that time, it was difficult to disentangle the independent effects of air pollution from the effects of other causes of disease outbreaks.

This report provides a comprehensive overview of the most credible evidence since the studies considered in that review (pre-November 2020). It should be noted that, as the pandemic is so recent, research into air pollution and COVID-19 is not as mature as other research areas, and further research will be necessary to confirm these emerging findings.

There are now a small number of studies of long-term exposure to air pollution with control for other factors related to COVID-19 at an individual level. These provide evidence that increased exposure to PM2.5 is related to increased hospitalization in those with COVID19. The results are less clear for deaths from COVID-19. There is some support for a relationship between long-term exposure to PM2.5 and NO2 and worse COVID19 outcomes from studies comparing different areas without control for other important factors at the individual level, although results from these studies may have other explanations. The data on long-term exposure to air pollution and numbers of cases is not entirely consistent.

Air pollution is known to increase amounts or severity of respiratory or cardiovascular disease and these diseases in turn are known to increase susceptibility to having more severe COVID-19. There are established biological mechanisms for the link between air pollution and disease in general.

The population studies of short-term exposure to air pollution and COVID-19 were inconclusive because the studies were generally of poor quality. On the other hand, a small number of good quality studies in animals have shown that air pollution (at higher doses than found in the environment) increases the number of receptors for the virus on lung cells. This evidence is at an early stage, but it suggests a possible mechanism by which air pollution could increase the likelihood of infection by the virus or worsening of COVID-19.

There is already a well-established link between air pollution and a range of infections in the lower part of the lung, (such as acute bronchitis and pneumonia). A review in this report found several studies from 2011-2021 showed a link between air pollution and hospital admissions for lung infections although the studies were spread across different age groups and disease definitions.

Particulate matter does not appear to play any important part in transporting COVID-19 in the environment, as had been suggested by some earlier studies.

Whilst this study highlights that more research is needed in this area, it is already clear that tackling air pollution is important in reducing the vulnerability of the population to COVID-19, and other infections like it.

Download the full report: Investigating links between air pollution and COVID-19 Report (PDF)

The review did not cover changes in air pollution exposures as a result of measures to control the pandemic in any detail but more information on this area can be found in Annex 1 Changes in air pollution exposure as a result of pandemic measures (PDF).