More than 40 scientists, including leading epidemiologists studying COVID-19, are calling on a top journal to retract a paper from a Nobel Prize–winning chemist that claimed that wearing face masks is the crucial factor in slowing the spread of the coronavirus — diminishing the role that social distancing measures play in protecting the public.
The scientists, who sent a signed letter to the journal PNAS on Thursday, say that the paper is based on false statements and flawed statistical analysis and could encourage people to put themselves at risk by congregating in groups, believing that wearing a mask is enough to protect them from infection.
“One of the things we really worry about is that people will take this as rigorous science and base their actions on it,” Noah Haber, a postdoctoral researcher at Stanford University who helped organize the letter calling for the paper’s retraction, told BuzzFeed News.
The paper was published on June 11 in PNAS, the flagship journal of the prestigious National Academy of Sciences, by researchers including Mario Molina of the University of California, San Diego. Molina is an atmospheric chemist who shared the 1995 Nobel Prize in Chemistry for his research showing how chemicals called CFCs, once widely used in aerosol sprays and as refrigerants, were destroying the ozone layer that protects us from the sun’s damaging ultraviolet rays.
As scientists have learned more about the role people without visible symptoms play in spreading the disease, health officials have recommended widespread use of face coverings. And a systematic review of the available evidence published on June 1 in the Lancet concluded that wearing masks “could result in a large reduction in risk of infection.”
Molina’s PNAS paper went much further, however, claiming that airborne transmission through microscopic droplets is the “dominant” way in which the coronavirus spreads. Molina’s team also estimated that rules requiring the wearing of masks prevented at least 66,000 coronavirus infections in New York City between April 17 and May 9, and 78,000 infections in Italy between April 6 and May 9.
Neither of those conclusions is justified by the evidence, the paper’s critics say. Still, the findings were shared widely on social media and covered uncritically by some news outlets including Forbes and the Los Angeles Times.
Soon after the paper appeared online, other scientists started posting eviscerating critiques of its assumptions and methods on Twitter. “There were just so many errors and issues with the paper that it almost seemed hard to know where to start,” Kate Grabowski, an epidemiologist at Johns Hopkins University who signed the letter calling for the study’s retraction, told Buzzfeed News.
On June 12, Grabowski posted that four scientists with the 2019 Novel Coronavirus Research Compendium, an expert group formed at Johns Hopkins to provide assessments of new research on the virus, had reviewed the paper and agreed that it should be retracted.
“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,” the letter says. “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.”
The biggest problem with the paper, according to Grabowski, is that its conclusions about the effectiveness of mask-wearing, compared to other measures to slow the spread of the virus, are based on false statements.
Molina’s team assumed that the only difference between New York City and the rest of the US in terms of regulatory measures to limit the spread of COVID-19 was a mandate that people should wear face coverings outside the home, introduced in New York City on April 17. The paper also stated: “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.”
Neither of those assumptions is true, Grabowski and other signatories say, which means the conclusion that mask-wearing is the crucial intervention just doesn’t hold up.
“There was a patchwork of varying behaviors and rules with varying degrees of adoption,” Daniel Larremore, a computational biologist at the University of Colorado at Boulder, who also signed the letter, told BuzzFeed News. He is studying data on people’s movements provided by Facebook and other technology companies, and has found that some people continued to move around even when stay-at-home orders were in place.
The letter requesting the paper’s retraction also slams the statistical methods used by Molina’s team. The researchers fitted straight lines to curves showing the growing number of cases, noted the timing of any mandate to wear face masks, and then looked at how the slope of the curve became more shallow after that. But this ignores the fact that case curves for infectious diseases tend to naturally level out after a certain period of time — which means it’s impossible to attribute the change to face masks alone.
Molina’s team also ignored the lag of one to two weeks, caused by the disease’s incubation period and delays in diagnosis, needed to see any noticeable effect on case numbers after a policy change.
Contacted by BuzzFeed News before the letter requesting retraction was sent to PNAS, Molina rejected criticisms of his paper. “We just looked at the data that is published and it’s surprisingly linear until something happens,” Molina told BuzzFeed News.
Molina argued that epidemiologists have overlooked the importance of microscopic droplets containing the virus. Specialists in air pollution, he argued, are used to thinking about the dangers of aerosols of tiny particles. “This is obvious to people who deal with air quality,” he said. “The only thing new here is that we apply this to the coronavirus.”
Other authors of the paper include Renyi Zhang, a former student of Molina’s who is now a professor of atmospheric chemistry at Texas A&M University in College Station, and his daughter Annie Li Zhang, who was an undergraduate student in chemistry at the University of Texas at Austin.
Renyi Zhang declined to speak to BuzzFeed News. “This paper is a peer-reviewed scientific publication. Its content can be debated in a legitimate, scientific fashion. However, we prefer not to engage in scientific debates via social media platform,” he told BuzzFeed News by email, referring to criticisms of the paper on Twitter.
Annie Li Zhang did not respond to requests for comment on her role in the research.
The fight over the paper also exposes long-running concerns about a quirk of the journal PNAS that allows members of the academy, like Molina, to bypass the normal mechanism of peer review, by which journal editors select independent scientific experts to vet a paper for publication.
Under the journal’s “contributed track,” academy members can submit up to two papers a year for which they select the reviewers themselves. Some scientists have criticized the practice as an anachronism that allows the publication of substandard work and perpetuates the image of the academy as an “old boys’ club.” The letter requesting the retraction of the paper also calls on PNAS to “reassess the Contributed Submission editorial process by which it was published.”
Academy members have so far been unwilling to give up this perk, but over the years the rules for the contributed track have been tightened, reducing how frequently it can be used. Journal policies also demand that “the subject matter must be within the member's area of expertise.”
Yet none of the authors of Molina’s paper, and neither of the reviewers, are experts in infectious disease epidemiology.
Responding to queries from BuzzFeed News before the letter requesting retraction, PNAS Editor-in-Chief May Berenbaum, an evolutionary biologist at the University of Illinois at Urbana-Champaign, said by email that she was aware of the criticisms of the paper.
“There are ongoing discussions about the paper among members of the journal leadership team, members of the Editorial Board, and other NAS members,” she said, adding that she was “awaiting additional information” on whether the publication of the paper had complied with the rules for the contributed track.
Berenbaum did not immediately respond to a request for comment about the letter calling for the paper’s retraction.
This is not the first controversy surrounding research on COVID-19, as scientists from many fields have rushed in to respond to the crisis. In the early days of the pandemic, there was widespread concern that “preprints” of studies, posted online without peer review, were stoking misinformation and panic. In April, a high-profile Stanford antibody study released as a preprint was criticized for its flawed methodology and undisclosed conflict of interest.
And earlier this month, high-profile papers published in the Lancet and the New England Journal of Medicine were retracted after Surgisphere, a small company that claimed to have provided health records collected from tens of thousands of patients, was unable to disclose the data behind the studies.