An Open Letter to the residents of East Longmeadow, the Town Council and Town Manager of East Longmeadow, and the East Longmeadow Board of Health

To whom it may concern:

Recently it has come to my attention that Justin McCarthy, an East Longmeadow resident, has filed a petition the the Town Council that has 160 signatories (or just over 1.25% of registered EL voters) “demanding an end to the defunct Health Board’s mask mandate”.

Justin lays out his arguments in a blog post from October 6, 2021, “Why the East Longmeadow Town Council Can and Should End the Mask Mandate.

I am not an expert in the law, therefore I will not comment on the strengths or flaws in Mr. McCarthy’s legal arguments, however, it is my understanding from talking to several other lawyers that his legal arguments are without merit.

However, I do have expertise in statistical analysis.  My training includes an M.S. in Applied Statistics from WPI in 2005, a Ph.D. in Statistics from the University of Connecticut  in 2011, a postdoctoral research fellow in the School of Public Health at the University of Massachusetts from 2011-2014.  Since 2014 I have been at Loyola University Chicago in the Department of Mathematics and Statistics where I am an Associate Professor of Statistics with tenure and the Director of the Data Science Program.  Given my particular background, I feel I am qualified to comment on Mr. McCarthy’s contention that the statement from the Health Board that was used to justify the mask order is not supported by any sort of data or evidence.  Specifically, Mr. McCarthy states in his blog post from October 6, 2021:

The Health Board justified its mask order by stating “we know that masks slow or prevent transmission of all COVID-19 variants so far.”  (See the third paragraph of the order.) The statement is not supported by any sort of data or evidence.

To put it bluntly, this statement is patently incorrect, and I will provide comprehensive support for masking policies later.  Before that, however, I want address he shortcomings in Mr. McCarthy’s framing of masking efficacy in relation to COVID-19.  Mr. McCarthy cites a single paper, Guerra and Guerra (2021) in International Research Journal of Public Health (DOI: 10.28933/irjph-2021-08-1005). (Note: Mr. McCarthy states in his October 6 blog post that Dr. Damien Guerra is a “bio-statistician [sic]”.  This is another incorrect statement.  Dr. Guerra is a trained biologist focusing on cell and molecular biology who appears to have taught biostatistics courses in the past.  It is unclear what his formal training in statistics is, if any.)  In that article, the authors conclude:

We did not observe association between mask mandates or use and reduced COVID-19 spread in US states. COVID-19 mitigation requires further research and use of existing efficacious strategies, most notably vaccination.

After reading the full article, it is my professional opinion that the statistical analysis performed in this article are extremely weak.  They used observational data (true randomized control trials (RCT), the gold standard for evaluating efficacy of a treatment are difficult to conduct for mask usage due to practical and ethical concerns) aggregated at the state level and looked for differences in growth rates associated with mask mandates.  However, the statistical methods that they chose to use are elementary and in my opinion not appropriate for this type of analysis (I am happy to elaborate if there is interest).

Curiously, one of the authors of this study, Damian Guerra, has written a letter to the East Longmeadow Town Council and Town Manager offering the following summary points based on an annotated bibliography: 

  • COVID-19 is a serious pandemic disease that warrants precautionary measures.

  • The best protections against COVID-19 are vaccination, ventilation, and generally good health (e.g., vitamin D repletion).

  • General civilian mask use and mask mandates likely do not reduce rates of COVID-19 transmission.

  • Studies purportedly demonstrating mask efficacy have used small sample sizes, have lacked comparison groups, or have omitted key information.

  • Among masks, only properly fitted KN95 (or related N/R/P95 type) respirators have demonstrated protection against viral infection.

  • Enhanced building ventilation is more effective than mask wearing at aerosol dispersion.

I agree with the first two bullet points wholeheartedly, but the third statement statement “General civilian mask use and mask mandates likely do not reduce rates of COVID-19 transmission” is simply not supported by evidence.  The fourth bullet point may have been at least partially true earlier in the pandemic, but at this point (October 2021) this is simply false.  The fifth bullet point is false, and the sixth bullet point is true, but simply wearing a mask is a much more easily implementable prevention measure than modifying existing building ventilation.

I will now address the contention from Guerra that “General civilian mask use and mask mandates likely do not reduce rates of COVID-19 transmission”.  Early in the pandemic, the evidence that masking reduced the the spread of COVID-19 was mixed.  There simply were not many good studies evaluating the effectiveness of mask at preventing the spread of COVID-19 because this is a novel virus that was only recently identified. However, as of October 2021, this is no longer the case.

(Note: In Guerra’s letter to the East Longmeadow, he mentions Vitamin D repletion as a “proven strategy for Covid-19 mitigation”.  Recent work from McGill University was unable to find any link between Vitamin D Covid mitigation.  The Authors state in their conclusion: “In this 2-sample MR study, we did not observe evidence to support an association between 25OHD levels and COVID-19 susceptibility, severity, or hospitalization. Hence, vitamin D supplementation as a means of protecting against worsened COVID-19 outcomes is not supported by genetic evidence. Other therapeutic or preventative avenues should be given higher priority for COVID-19 randomized controlled trials.”)

In January 2021, a review article entitled “An evidence review of face masks against COVID-19” by Howard et. al. was published in the Proceeding of the National Academy of Sciences of the United States of America (PNAS).  This article presents an even handed review of the available evidence of the efficacy of mask use in limiting the spread of COVID-19.  They conclude:

Our review of the literature offers evidence in favor of widespread mask use as source control to reduce community transmission: Nonmedical masks use materials that obstruct particles of the necessary size; people are most infectious in the initial period postinfection, where it is common to have few or no symptoms (4546141); nonmedical masks have been effective in reducing transmission of respiratory viruses; and places and time periods where mask usage is required or widespread have shown substantially lower community transmission.

(Note: In a separate blog post, Mr. McCarthy, who, I will remind you, is not an economist, contends that the mask mandate is having a negative impact on local businesses.  He offers basically no evidence of this beyond a few scattered anecdotes, but if he is concerned about the economy, Howard et. al. mentions that “Economic analysis suggests that mask wearing mandates could add 1 trillion dollars to the US GDP.”)

For more evidence the use of masks in limiting the spread of COVID-19, the CDC has compiled (as on May 7, 2021) a list of studies evaluating the efficacy of masks.  In their conclusion, they state:

Experimental and epidemiological data support community masking to reduce the spread of SARS-CoV-2. The prevention benefit of masking is derived from the combination of source control and wearer protection for the mask wearer. The relationship between source control and wearer protection is likely complementary and possibly synergistic14, so that individual benefit increases with increasing community mask use. Further research is needed to expand the evidence base for the protective effect of cloth masks and in particular to identify the combinations of materials that maximize both their blocking and filtering effectiveness, as well as fit, comfort, durability, and consumer appeal. Mask use has been found to be safe and is not associated with clinically significant impacts on respiration or gas exchange. Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene, and adequate ventilation.

Notice that the CDC says “Further research is needed to expand the evidence base for the protective effect of cloth masks and in particular to identify the combinations of materials that maximize both their blocking and filtering effectiveness, as well as fit, comfort, durability, and consumer appeal.”  This is a sign of good, solid science.  When something is unknown and more evidence is needed, that is stated.  

As of the writing of that CDC summary (May 7, 2021) there is a preponderance of observational and epidemiological evidence that mask wearing effectively limits the spread of COVID-19.  However, there was no randomized controlled trial evaluating the causal effectiveness of masks in limiting COVID-19 spread, but just recently a large randomized-trial was performed to study exactly the question of mask efficacy.

On September 1, 2021, a working paper entitled “The Impact of Community Masking on COVID-19: A Cluster-Randomized Trial in Bangladesh” was published online. The authors of that study describe their experiment:

A randomized-trial of community-level mask promotion in rural Bangladesh during COVID-19 shows that the intervention tripled mask usage and reduced symptomatic SARS-CoV-2 infections, demonstrating that promoting community mask-wearing can improve public health.

This article finds statistically significant reductions in the spread of COVID-19 in villages where masks were worn compared to villages where masks were not worn.  In addition, they demonstrate that cloth masks also significantly lowered the spread of COVID-19 compared with villages that were not wearing masks.  It should be noted that the reduction in COVID-19 with cloth masks was smaller than the reduction observed when surgical masks were worn.  In the authors’ words:

We present results from a cluster-randomized controlled trial of a scalable intervention designed to increase mask-wearing and reduce cases of COVID-19. Our estimates suggest that mask-wearing increased by 28.8 percentage points, corresponding to an estimated 51,347 additional adults wearing masks in intervention villages, and this effect was persistent even after active mask promotion was discontinued. The intervention led to a 9.3% reduction in symptomatic SARS-CoV-2 seroprevalence (which corresponds to a 103 fewer symptomatic seropositives) and an 11.9% reduction in the prevalence of COVID-like symptoms, corresponding to 1,587 fewer people reporting these symptoms. The effects were substantially larger (and more precisely estimated) in communities where we distributed surgical masks, consistent with their greater filtration efficiency measured in the laboratory (manuscript forthcoming). In villages randomized to receive surgical masks, the relative reduction in symptomatic seroprevalence was 11% overall, 23% among individuals aged 50-60, and 35% among those over 60.

It is important to point out that currently, this article has not been peer-reviewed.  However, in my reading of the manuscript, it appears to be a well designed from a statistical perspective and the statistical methods are appropriate.  The Johns Hopkins School of Public Health made he following statement regarding the study (I would encourage everyone to read the full statement, including limitations that were identified):

This was a very large and well-designed cluster-randomized controlled trial of a multi-pronged intervention program to encourage mask-wearing in rural and peri-urban Bangladesh from November 2020 to April 2021; it was available as a preprint and is thus not yet peer reviewed. The study found that the intervention package (which included mask distribution, public role-modeling, and encouragement to non-mask-wearers in public settings) more than tripled public mask usage behaviors (from 13% to 42%) without diminishing observed physical distancing.


If the results are valid, they imply that near-universal mask wearing would be associated with much larger reductions in transmission.

In conclusion, there is very strong observational and epidemiological evidence that mask use, both cloth and surgical, in public reduces community spread of COVID-19, and I would recommend that local municipalities too continue to comply with state and federal masking guidelines, put in place by experts in public health, epidemiology, and medicine, as a part of a continued effort, along with vaccinations, social distancing, and basic hygiene, to combat COVID-19.  I would encourage everyone to read the American College of Pediatrics statement endorsing the use of facemarks for children 2 years of age and older.

Finally, while masks are an important par of COVID-19 prevention, the best weapon in our fight against this virus, and I think Dr. Guerra and I can both agree on this, is the safe and effective COVID-19 vaccine.  I would encourage everyone to get vaccinated and to say up to date on emerging guidelines for booster shots.

Stay safe.


Gregory J. Matthews, Ph.D.

Posted on October 11, 2021, in Uncategorized. Bookmark the permalink. Leave a comment.

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