Formal Request for the Retraction of “Identifying airborne transmission as the dominant route for the spread of COVID-19.” DOI: 10.1073/pnas.2009637117.

June 18, 2020
Proceedings of the National Academy of Sciences
500 Fifth Street, NW
NAS 340
Washington, DC 20001 USA
Dear Editorial Board of the Proceedings of the National Academy of Sciences,
We are writing with deep concerns about a paper recently published in your journal, entitled
“Identifying airborne transmission as the dominant route for the spread of COVID-19.” The paper made
extraordinary claims about routes of transmission, the effectiveness of mask-wearing, and by implication,
the ineffectiveness of other non-pharmaceutical interventions. While we agree that mask-wearing plays an
important role in slowing the spread of COVID-19, the claims in this study were based on easily
falsifiable claims and methodological design flaws. We present only a small selection of the most
egregious errors here. Given the scope and severity of the issues we present, and the paper’s outsized and
immediate public impact, we ask that the Editors of PNAS retract this paper immediately and reassess the
Contributed Submission editorial process by which it was published.
The main conclusions of this paper are based in comparison of linear case count slopes within and
between regions, with mask mandates as the observed variable of interest. It ignores other clear
differences in disease control policy between these areas, including broader heterogeneity in face mask
policy. In one critical example, the paper asserts that “after April 3, the only difference in regulatory
measures between NYC and the United States lies in face coverings on April 17 in NYC.” This is
verifiably false, based on widely available (e.g., HIT-COVID ) sources. It is flatly untrue that there were
no other regulatory differences between NYC and the rest of the US on those dates; it is also untrue that
NYC was the only region in the US mandating use of face coverings. In another example, the paper
asserts that airborne transmission is the dominant route for COVID-19 spread. To justify this headline
conclusion, the authors state that “With social distancing, quarantine, and isolation in place worldwide
and in the United States since the beginning of April, airborne transmission represents the only viable
route for spreading the disease.” In fact, in April, many regions (e.g., Sweden, parts of the United States)
were not in lockdown, and quarantine and isolation were not in place in most parts of the world. If
similarly false statements about exposure were made widely in a cohort study or a randomized control
trial, a rapid and complete retraction of the study would quickly follow. Hence, it is our view that PNAS
is obligated to issue retraction of this work on these grounds alone.
Beyond this, the study is afflicted with serious methodological errors that undermine any
confidence in its findings. These include the following: 1) The analysis ignored the lag between changes
in disease transmission and changes in reported case counts, 2) Dates of policy implementation are
extremely poor proxies for mass behaviors, including social distancing and mask use, 3) Dates of policy
implementation were concurrent with an enormous set of changes across society which plausibly affected
reported incidence of COVID-19, 4) Case counts were modeled with a simple linear regressions, which is
not consistent with infectious disease dynamics, 5) Demographics, policies, and contact behaviors in
Wuhan, Italy, New York City, and the USA are inappropriately treated as being nearly equivalent to one
1 Renyi Zhang, Yixin Li, Annie L. Zhang, Yuan Wang, Mario J. Molina. Identifying airborne transmission as the dominant route for the
spread of COVID-19. Proceedings of the National Academy of Sciences Jun 2020, 202009637; DOI: 10.1073/pnas.2009637117
another with respect to the epidemic, and 6) No measures of statistical uncertainty are measured or
presented, which is a departure from scientific norms and particularly concerning given an analysis based
on only three regions. Any one of the above issues in isolation would be cause for serious concern, but in
combination, they are alarming.
While masks are almost certainly an effective public health measure for preventing and slowing
the spread of SARS-CoV-2, the claims presented in this study are dangerously misleading and lack any
basis in evidence. Unfortunately, since its publication on June 11th, this article has been distributed and
shared widely in traditional and social media, where its claims are being interpreted as rigorous science.
As societies debate the risks of re-opening and relaxing social distancing measures, it is crucial that
decisions rely on a solid evidence base.
The scale, scope, and intensity of the issues in this paper and the immediacy of the decisions
being made based on its claimed conclusions do not make it amenable to either correction or extended
debate within the academic literature. Accordingly, we ask that the editorial board of PNAS retract this
paper immediately. Further, the scale of the methodological flaws raise concerns about the publication
process. For this reason, we would argue that it may be time for PNAS to reconsider its policies on the
Contributed Submissions track under which this paper was published, as this mechanism effectively
bypasses editorial decisions and undermines peer review. While these may be painful processes, we
believe that they constitute the best way forward in an extraordinary time for the scientific endeavor, and
more importantly, for the health and well-being of the public.
Noah Haber, ScD
Postdoctoral Fellow
Meta-Research Innovation Center at
Stanford University
Mary Kate Grabowski, PhD
Assistant Professor
Departments of Pathology and Epidemiology
Johns Hopkins University
Daniel B. Larremore, PhD
Department of Computer Science &
BioFrontiers Institute
University of Colorado Boulder
Nikolas Wada, PhD
Co-lead, Non-Pharmaceutical Interventions
Novel Coronavirus Research Compendium
Johns Hopkins University
Steven N. Goodman, MD, MHS, PhD
Professor of Epidemiology and Population Health,
and Medicine
Stanford University
Justin Lessler
Associate Professor
Department of Epidemiology
Johns Hopkins University
Cosignatories on the following pages
3 After 48 hours, AltMetrics placed this article’s global sharing and discussion in the top 5% of all research and the highest (#1 of
84,648) from PNAS.
Co-signed by (in alphabetical order):
Benjamin M Althouse, PhD, ScM, Epidemiology, Institute for Disease Modeling
Onyebuchi A. Arah, MD, DSc, PhD, Department of Epidemiology, UCLA
Cathrine Axfors, MD, PhD, Meta-Research Innovation Center at Stanford, Stanford University
Andrew S Azman, PhD, Department of Epidemiology, Johns Hopkins Bloomberg School of Public
Ana Bento, PhD, Department of Epidemiology and Biostatistics, School of public health, Indiana
Noel T. Brewer, PhD. Department of Health Behavior, Gillings School of Global Public Health,
University of North Carolina
Caroline Buckee, DPhil, Epidemiology , Harvard TH Chan School of Public Health
Sarah Cobey, PhD, Ecology and Evolution, University of Chicago
Natalie E. Dean, PhD, Department of Biostatistics, University of Florida
Holly Elser, PhD, Center for Population Health Sciences, Stanford University
Jeremy S. Faust, MD MS, Emergency Medicine, Brigham and Women’s Hospital, Harvard Medical
Jacqueline M. Ferguson, PhD MHS, Center of Population Health Sciences, Stanford University
Bailey K Fosdick, PhD, Department of Statistics, Colorado State University
Paul Glasziou, PhD, Institute of Evidence-based Healthcare, Bond University
David Robert Grimes, PhD, School of Physical Sciences, Dublin City University
Ben Harris-Roxas, PhD, Centre for Primary Health Care and Equity, UNSW Sydney
William P. Hanage PhD, Epidemiology, Harvard T. H. Chan School of Public Health
James A.J. Heathers, PhD, Bouve College of Health Sciences, Northeastern University
Eloise A.C. Howse, BA (Hons) MPH, School of Public Health, The University of Sydney
Mathew V. Kiang, ScD, Center for Population Health Sciences, Stanford University
Stephen M. Kissler, PhD, Department of Immunology and Infectious Diseases, Harvard T.H. Chan
School of Public Health
Eric T. Lofgren, MSPH PhD, Paul G. Allen School for Global Animal Health, Washington State
Pamela P. Martinez, PhD, Department of Epidemiology, Harvard School of Public Health
Heather McKay, PhD, Epidemiology, Johns Hopkins Bloomberg School of Public Health
C. Jessica E. Metcalf, PhD, Ecology and Evolutionary Biology, Princeton University
Gideon Meyerowitz-Katz, BSc MPH, School of Health and Society, University of Wollongong
Alice Milivinti, PhD, Center for Population Health Sciences, Stanford University
Michael J. Mina, MD, PhD, Department of Epidemiology, Harvard T.H. Chan School of Public Health
C. Brandon Ogbunu, PhD, Department of Ecology & Evolutionary Biology, Yale University
Lesley S. Park, PhD, MPH, Center for Population Health Sciences, Stanford University
Daniel W Reeders, School of Regulation and Governance, Australian National University
David H. Rehkopf, ScD, MPH, School of Medicine, Stanford University
Christopher T. Rentsch, PhD, Faculty of Epidemiology and Population Health, London School of
Hygiene and Tropical Medicine
Isabel Rodríguez-Barraquer, MD, PhD, Department of Medicine, University of California, San Francisco
Samuel V. Scarpino, PhD, Network Science Institute, Northeastern University
Emily R. Smith, ScD, MPH, Department of Global Health, George Washington University
Sarah E. Wieten, PhD, Stanford Center for Biomedical Ethics, Stanford Health Care
Mollie E. Wood, PhD, Department of Epidemiology, Harvard T.H. Chan School of Public Health
Trent Yarwood, BAppSc MBBS MPHTM FRACP, Infectious Diseases, Cairns Hospital

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