Initially High Correlation between Air Pollution and COVID-19 Mortality Declined to Zero as the Pandemic Progressed: There Is No Evidence for a Causal Link between Air Pollution and COVID-19 Vulnerability

Round 1

Reviewer 1 Report

[IJERPH] Manuscript ID: ijerph-1847150 - Review Report

 

Authors reported on a very interesting study on Correlation between air pollution and COVID-19 mortality over a long term. The manuscript is generally well written, and the rationale, objectives and methodology are clearly presented. Furthermore, the study objectives are promising and important for the fields of air pollution and the recent COVID -19 pandemic. The manuscript brings up some very interesting concepts in the scientific community. For example the importance of replication within the scientific community as well as the importance of long term trends when it comes to air pollution studies.

I recommend the authors tone down on some of the language use such as “confuse” and causality. The authors described Wu et al study as confusing their results (short term trends) with long term trends. Whereas air pollution–mortality estimates are generally larger at longer-term, compared with short-term, exposure time scales, It is also important to note that short term time scales air pollution studies are equally as important to long term studies when it comes to interventions.

 

Below are some comments for the authors

 

 Abstract

Lines 12-13 : Authors should state the estimate in addition to the C.I Authors only report CI

 

Introduction

Lines 21-40 : Authors do a great job by summarizing previous studies on the association between air pollution and COVID 19. Authors should consider adding a statement to these studies informing the reader if these studies were short term trends  or long term trends

 

Lie 42 : Authors should provide the exact date range Wu etal conducted their study( eg from January 2020 to June 2020?)

 

Line 70-77 : Did the authors just used  average county-level PM2.5 concentration from 2000 to 2016 similar to what Wu et al used when they extended their analysis? Authors need to be transparent to the reader here. Authors should mention the time frame of PM2.5 data used when they extended Wu et al study

 

Iines 95-100 : because the authors  did not  disclose the time frame of the air pollution data used in the extended analysis, it is difficult to conclude that the decline in the association of COVID-19 was  associated with air pollution

 

Lines 102-104. Did Wu et al mentioned that their findings was as a result of a causality? If not then why do the authors include the statement ….” association was particular to one phase (the first phase) of the pandemic 103 and does not represent an important causal relationship between air pollution and 104 COVID-19 mortality.” Can the authors explain why they are assuming causality here?

 

Lines 106: “Wu et al. confused short-term trends in the spread of COVID and long-term trends  in COVID mortality.” The authors should consider toning down with the use of the word confused . At the time Wu et al conducted their study, that was the result they found using data within that time frame.

 

 

Line 144 to 146: good paragraph

 

 

Results

 

Authors should consider performing a set of sensitivity analysis by

a. adjusting for years.

 

b. Author should also consider performing another analysis from September 2020 to May 2022 and compare the results. That is there are going to be three results to compare at different time frames ( the Wu et tal study, an analysis from September 2020 to May 2022 and another analysis from Wu etal to May 2022 which they already did and presented the results)

 

 

 

Discussion

Authors should consider dedicating a whole paragraph on the importance of long trend time scales when it comes to air pollution and health effects

 

Author Response

Thank you so much for you helpful suggestions. Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript "Correlation between air pollution and COVID-19 mortality: initial happenstance, not causality" addresses an important issue: the relationship between PM_2.5 concentrations and COVID-19 mortality rates. The authors replicated the method used by Wu et al. and found, as previously published, a positive association between air pollution and COVID-19 mortality over the period analyzed by Wu et al., i.e., April to September 2020. However, when they extended the study period through May 2022 a sharp decline in the association of PM_2.5 air pollution with COVID-19 after September 2020 was found.

The objectives were clearly stated and explained in the manuscript, and the experimental strategy was appropriate to gather the experimental information from which the conclusions were drawn. The manuscript is well written and has good organization. The authors have done a great job on analyzing the experimental data and on discussing the results, considering always different alternative explanations/considerations for interpreting the results.

 

Some minor points deserve careful attention:

1.      The scale in Figure 2, a replication of Figure 1 (From Wu et al.), although more pleasant to look at than the original Figure, doesn’t display the exact same scale on the Y-axis. This is not a big inconvenience but I would suggest to apply the same exact scale.

2.      The shaded color of the 95% confidence interval in Figure 3 from Sep 2020 to May 2022 is difficult to appreciate and may not be the most appropriate.

3.      Throughout the manuscript there are missing subscripts and superscripts in almost all units of measurement. For example: in line 13 “1 mg/m3” should be changed to “1 mg/m³”; in line 34 PM2.5 should be changed to “PM_2.5”; and so on. This is surely a formatting issue but must be addressed in the final version of the article.

4.      In line 162, in the last sentence of the paragraph I feel like a “be” is missing.

5.    Please comment on the initial association of COVID-19 mortality with air pollution within the earliest phase until September 2020 and the possible reasons for this association in the Discussion.

Author Response

Thank you so much for you helpful suggestions. Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

-I suggest that from the title indicate that it was carried out in the study. As it is, the title is not informative of what was done in the study.

-The authors should delve into the justification for carrying out the study, even more so when a replication and extension of previously published data is carried out.

-The authors must clearly state what the objective of the study was.

-The horizontal axis of figure 1 must be corrected since it looks very stacked, which prevents its interpretation.

-Have the authors obtained permission from Wu et al. to post figure 1?

-Authors should include the limitations of an ecological study.

-It is suggested to carry out a more current review of the literature incorporating bibliography on the association studied. Considering that to date it is considered a relationship that has important limitations.

-Extend the discussion with more recent studies that have evaluated the correlation studied.

Author Response

Thank you so much for you helpful suggestions. Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

1 The contribution is little.

2 The author replicated Wu et al.’s results. Why?

Author Response

Thank you so much for you helpful suggestions. Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

I consider that the authors have addressed all the observations made.

Reviewer 4 Report

It can be acccept