November 4, 2020

expert reaction to study looking at air pollution and COVID-19 mortality

A study published in Science Advances looks at exposure to air pollution and COVID-19 mortality in the United States.

Dr Mark Miller, BHF Senior Research Scientist, University of Edinburgh, said:

“This is a study by Wu and colleagues is an elaboration on their earlier work following peer-review by expert scientists in the area.

“The authors find higher levels of covid-19 cases in counties of the USA which have higher levels of pollution particles in the air. It is striking that only small differences in the levels of particles are linked to significantly higher levels of covid-19.

“The links between air pollution and Covid-19 are assessed at a regional level. While this does not allow a full assessment of the factors that could account for the association, the authors have done an excellent job in describing other possible factors that could influence their results. These are challenging issues to address because of the complicated situation of the pandemic and the changes in people’s behaviour as the awareness of situation emerged.

“This work adds to a growing number of studies finding a link between air pollution and covid-19, and provides clarity for future studies that can look in more detail at which pollutants are driving these changes and what the benefits could be of different measures to reduce these pollutants.

“We now need a better understanding of the biology underlying these associations. Could these findings simply be because both air pollution and covid-19 affect the same vulnerable groups – the elderly and those with respiratory of cardiovascular disease – or is there something more going on? Could coronavirus and air pollution be have additive effects to increase the risk of death in these individuals? Could it be that airborne particles carry the virus or help it gain access to the cells of our body?

“The levels of air pollution in this study were fairly modest. Therefore, while this study is carried out in the USA, there is no reason to believe that a similar situation wouldn’t occur in the UK, or anywhere else in the world.

“Overall, these findings highlight a link that urgently needs further study to understand if this increased risk is a direct result of air pollution and if so, how this occurs. This could have serious consequences in, for example, those with heart disease, who are already very vulnerable to the detrimental effects of air pollution.”

Prof Anna Hansell, Professor in Environmental Epidemiology, Director of the Centre for Environmental Health and Sustainability, and Director of the NIHR Health Protection Research Unit in Environmental Exposures and Health, University of Leicester, said:

“This analysis, by an internationally respected air pollution research group from Harvard, is an update of one available on the preprint server Medrxiv since April (https://www.medrxiv.org/content/10.1101/2020.04.05.20054502v2 ) and extensively commented on in the press at that time. The study examines COVID-19 mortality at county level in the US, taking account of factors that might affect and ‘skew’ the observed links. This peer-reviewed version does not appear to have changed substantially except that the time period covered now extends to mid- June 2020. This has resulted in a small change to the observed association between air pollution and mortality – the authors now report that an increase of 1 ug/m3 in the long-term average particulate PM2.5 exposure is associated with an 11% (95% CI, 6 to 17%) increase in COVID-19 mortality. This is compatible with the 8% increase reported in the initial preprint using data to April.

“It is an extremely well conducted study of its type, with full details of the analysis given in the comprehensive appendix. The article itself concentrates on how to interpret the study design – it is an ecological study that looks at the association between air pollution and COVID-19 mortality at the group level. It is of concern that associations seen with COVID-19 were an order of magnitude higher than for associations between air pollution and all-cause mortality. However, as the authors acknowledge, this is a preliminary study requiring further follow-up studies at individual level before being able to confirm findings.

“Such studies are important when considering air pollution policy and, in the final paragraph of the paper, the authors raise the relevance of these to revisions of US Air Quality Standards. The US context is important here –  roll backs of Environmental Protection Agency (EPA) air quality rules and regulations under the Trump administration (https://www.nytimes.com/interactive/2020/climate/trump-environment-rollbacks-list.html ) and also that the EPA temporarily stopped enforcing certain environmental monitoring and reporting requirements between March 13 and August 31 2020 due to COVID-19  (https://www.epa.gov/enforcement/covid-19-implications-epas-enforcement-and-compliance-assurance-program). The outcome of the current US election is likely to influence air pollution exposure of US citizens for years to come.”

‘Air pollution and COVID-19 mortality in the United States: Strengths and limitations of an ecological regression analysis’ by X. Wu et al. was published in Science Advances at 18:00 UK time on Wednesday 4^th November.

Declared interests

Prof Anna Hansell: “I am a member of the Committee on the Medical Effects of Air Pollution (COMEAP), but my comments here are in a personal capacity as Professor in Environmental Epidemiology at the University of Leicester. I have no conflicts of interest to declare.”