By Anya Nanning Ramamurthy – 

COVID-19 has dominated media, and changed our way of life for nearly two years (Figure 1), but this has not been felt evenly by everyone. For instance, COVID-19 mortality rates are higher for men [1], and older people and some ethnic groups are more vulnerable [2,3]. Those with certain pre-existing health conditions, including chronic respiratory diseases, face higher risk [4]. Now, a new study by Travaglio et al. proposes a causal link between chronic air pollution and COVID-19 risk.

Figure 1: COVID-19 has dominated our lives for two years. Lofhi, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Respiratory problems are common in COVID-19 [5]. Chronic exposure to air pollutants, including nitrogen oxides, ozone, and other common road transport pollutants, induces and exacerbates respiratory and cardiovascular conditions [6]. Travaglio et al. argue that even small increases in air pollution result in large increases in COVID-19 risk [4].

This research looked at UK data for both air pollution (nitrogen oxides, ozone, and particulates) and COVID-19 infections and deaths. Previous studies, in Northern Italy [7], Europe [8], and the USA [9] used local and regional level data, to find a positive correlation between air pollution and COVID-19 risk. Using data from the UK Biobank, Travaglio et al. went further, studying this connection at an individual level, providing further compelling evidence of the link.

Using individual level data is particularly important in considering infectivity in a disease like COVID-19 since high proportions of cases are asymptomatic and therefore not included in the regional and local data pools.

Epidemiological data can be difficult to interpret with certainty because many different demographic factors come into play. However, the authors argue that even after allowing for factors including population density and mean annual earnings, the connection between increased air pollution and COVID-19 infectivity is evident [4].

An increase in exposure to particulate matter was also connected with increased risk of COVID-19 infection [4]. Travaglio et al. propose some mechanisms for this link. For example, they argue their findings support the theory that viruses like COVID-19 affix themselves to air pollutants, possibly explaining increased infectivity.

So, what pollutants were linked with increased COVID-19 related mortality? Travaglio et al. found compelling evidence for a link between increased nitrogen oxides (NOx) levels and COVID-19 risk. Even small increases of long-term nitrogen oxides (1μg/m3 ,which is roughly the same amount as is permitted under the Ontario Drinking Water Standards [10]) correlated with increased COVID-19 related mortality of between 1.5% and 2.5%. For ozone, the picture was less clear, showing a positive correlation at the regional level only. However it is well known that NOx and ozone readily interconvert [10] and the authors recognise that differences in the conversion rates in urban areas may account for this discrepancy.

More research is needed; however, the findings are significant in providing evidence of the importance of reducing air pollution in order to reduce the risk of COVID-19, and to prepare for and mitigate potential impacts of future pandemics and epidemics, which are likely to increase due to climate change. These findings are therefore relevant and important in guiding both health and emissions policies, along with developing disease management strategies.

References and further reading

[1] Peckham, H., de Gruijter, N.M., Raine, C. et al. (2020) Male sex identified by global COVID-19 meta-analysis as a risk factor for death and ITU admission. Nat Commun, 11 (1), 1-10.

[2] Yanez, N.D., Weiss, N.S., Romand, JA. et al. (2020) COVID-19 mortality risk for older men and women. BMC Public Health, 20 (1), 1-7.

[3] ONS (2020). Why have Black and South Asian people been hit hardest by COVID-19?https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/articles/whyhaveblackandsouthasianpeoplebeenhithardestbycovid19/2020-12-14 [27/11/21]

[4] Travaglio, M., Yu, Y., Popovic, R., Selley, L., Santos Leal, N., Miguel Martins, L. (2021) Links between air pollution and COVID-19 in England. Environmental Pollution, 268 (115859).

[5] Huang, C., Wang, Y., Li, X., Ren, L., Zhao, J., Hu, Y., Zhang, L., Fan, G., Xu, J., Gu, X., Cheng, Z., Yu, T., Xia, J., Wei, Y., Wu, W., Xie, X., Yin, W., Li, H., Liu, M., Xiao, Y., Gao, H., Guo, L., Xie, J., Wang, G., Jiang, R., Gao, Z., Jin, Q., Wang, J., Cao, B. (2020) Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. The Lancet, 395 (10223), 497-506.

[6] Jiang, X., Mei, X., Feng, D., (2016) Air pollution and chronic airway diseases: what should people know and do?. Journal of Thoracic Disease, 8(1), E31.

[7] Conticini, E., Frediani, B., Caro, D. (2020) Can atmospheric pollution be considered a co-factor in extremely high level of SARS-CoV-2 lethality in Northern Italy?. Environmental Pollution, 261 (114465)

[8] Ogen, Y. (2020) Assessing nitrogen dioxide (NO2) levels as a contributing factor to coronavirus (COVID-19) fatality. Science of The Total Environment, 726 (138605)

[9] Wu, X., Nethery, R C., Sabath, M B., Braun, D., Dominici, F. (2020) Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study. Science Advances

[10] McKague, K., Reid, K., and Simpson, H. (2007) Environmental Impacts Of Nitrogen Use In Agriculture. Ontario Ministry of Agriculture, Food and Rural Affairs

http://www.omafra.gov.on.ca/english/engineer/facts/05-073.htm

[11] Air Pollution Information System (2021) Nitrogen Oxides (NOx). http://www.apis.ac.uk/overview/pollutants/overview_nox.htm [05/12/21]