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

Research, published in Cardiovascular Research, looked at exposure to air pollution and the risk of death from COVID-19.


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:

Technical details

“This new paper uses data on long-term outdoor air pollution exposures worldwide and estimates number of COVID-19 mortality associated with these, using exposure-response coefficients (of air pollution association with COVID-19 deaths) from two other studies.  The two studies the coefficients come from are references 7 and 17 in the paper.  The first is a US study by one of authors, that was first released in preprint format in April and widely covered in the press.  While a carefully conducted study, it was conducted at US county level and may not fully adjust for all relevant factors at individual level.  Further, it has not yet completed the full peer review process, so size of associations reported may change after reviewers’ comments.  The second study relates to SARS in China in 2003 and not to COVID-19.  The SARS analysis has a number of limitations, most notably, analysis was at the level of region in China and did not account for confounding effect of other factors.

“A further comment is that both papers used for the present study are ecological or group-level studies.  Ecological studies are generally regarded as hypothesis-generating rather than confirmatory.  This means that the estimates of the size of any relationship between air pollution and COVID-19 deaths may not be precise.

“There are only a small number of total available studies directly investigating relationships between air pollution and COVID-19 to date, which are not consistent and there are various issues with design and interpretation.


“While it is extremely likely that there is a link between air pollution and COVID-19 mortality, it is premature to attempt to precisely quantify it (as here), given the current state of the evidence.

“However, there are plenty of other good reasons to act now to reduce air pollution, which the WHO already links to 7 million deaths worldwide per year (4.2 million of these linked to outdoor air pollution and the remainder to indoor air pollution).”



‘Regional and global contributions of air pollution to risk of death from COVID-19’ by Andrea Pozzer et al. was published in Cardiovascular Research at 00:05 UK time on Tuesday 27 October 2020.

DOI: 10.1093/cvr/cvaa288



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.”




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