Tuesday, November 10, 2020

Revisiting March 2020: What Were Epidemiologists Thinking about Masks?

A basic part of building credibility is not to flip-flop on your advice. But early in the pandemic, public  health authorities at first advised against wearing masks, and then shifted over to recommending but not requiring masks. Now masks are required in many states in public and indoor settings. What were public health authorities and epidemiologists thinking when they were recommending against masks? 

As one example of such a recommendation, the World Health Organization published on January 29, 2020, "Advice on the use of masks in the community, during home care and in health care settings in the context of the novel coronavirus (‎‎‎‎‎‎2019-nCoV)‎‎‎‎‎‎ outbreak: interim guidance." Here's a taste of the recommendations: 
Wearing a medical mask is one of the prevention measures to limit spread of certain respiratory diseases, including 2019- nCoV, in affected areas. However, the use of a mask alone is insufficient to provide the adequate level of protection and other equally relevant measures should be adopted. If masks are to be used, this measure must be combined with hand hygiene and other IPC measures to prevent the human-to-human transmission of 2019-nCov. ... Wearing medical masks when not indicated may cause unnecessary cost, procurement burden and create a false sense of security that can lead to neglecting other essential measures such as hand hygiene practices. Furthermore, using a mask incorrectly may hamper its effectiveness to reduce the risk of transmission. ... [In a community setting,] a medical mask is not required, as no evidence is available on its usefulness to protect non-sick persons. ... Cloth (e.g. cotton or gauze) masks are not recommended under any circumstance.
Early recommendations from US health officials also tended to downplay the usefulness of masks. Jack Brewster offers a review of the timeline in Forbes
February 27
One day after the Centers for Disease Control confirmed the first possible instance of Covid-19 “community spread,” CDC Director Robert Redfield is asked at a hearing on Capitol Hill whether healthy people should wear a face covering and responds, “No.”

February 29
On the same day public health officials announce the first death in the United States from Covid-19, U.S. Surgeon General Jerome Adams orders Americans to “STOP BUYING MASKS!” in an all-caps message on Twitter, claiming they are “NOT effective in preventing [the] general public from catching coronavirus” and will deplete mask supplies for healthcare providers.

March 8
During an interview with 60 Minutes—an interview Trump and his allies cite as an example of when the doctor was wrong—Fauci says "there's no reason to be walking around with a mask,” though adds he’s not “against masks,” but worried about health care providers and sick people “needing them,” and says masks can lead to “unintended consequences” such as people touching their face when they fiddle with their mask.
By late March and early April, US health public health authorities were beginning to recommend wearing masks in settings with other people. But the World Health Organization in its updated April 6 guidance continued to express uncertainty about average people wearing masks in public, emphasizing that medical masks should be reserved for health care workers and that "As described above, the wide use of masks by healthy people in the community setting is not supported by current evidence and carries uncertainties and critical risks." However, by June 5 the WHO had altered its guidance, now saying: 
The use of masks is part of a comprehensive package of the prevention and control measures that can limit the spread of certain respiratory viral diseases, including COVID-19. Masks can be used either for protection of healthy persons (worn to protect oneself when in contact with an infected individual) or for source control (worn by an infected individual to prevent onward transmission). However, the use of a mask alone is insufficient to provide an adequate level of protection or source control, and other personal and community level measures should also be adopted to suppress transmission of respiratory viruses. Whether or not masks are used, compliance with hand hygiene, physical distancing and other infection prevention and control (IPC) measures are critical to prevent human-to-human transmission of COVID-19. ... the use of non-medical masks, made of woven fabrics such as cloth, and/or non-woven fabrics, should only be considered for source control (used by infected persons) in community settings and not for prevention.
Toward the end of August, I tried to summarize the state of the research evidence about masks. Here, I just want to note that when there is such a dramatic switch in public health recommendations, from saying that masks in general aren't helpful all the way to requiring them in a few months, it raises an obvious question: What were they thinking? 

In the most recent issue of the Journal of Economic Perspectives, epidemiologist Eleanor J. Murray offers an honest and open answer to the question (Fall 2020, "Epidemiology’s Time of Need: COVID-19 Calls for Epidemic-Related Economics"). Rather than try to summarize her nuanced view, I'll just quote from her paper: 
In January 2020, there was strong evidence supporting the use of personal protective equipment, including face masks, in high-risk settings such as health care facilities for the prevention of respiratory infections. However, the existing epidemiologic literature on the use of face masks by the general public for control of respiratory infections was extremely limited and showed mixed results (Brosseau 2020; Brosseau and Sietsema 2020; Chu et al. 2020). For example, one meta-analysis found that mask use in health care approximately halved the risk of influenza infection (Saunders-Hastings et al. 2017), and a randomized trial of non-pharmaceutical interventions in the home found an approximately 20 percent reduction in influenza infection for households using both face masks and hand sanitizer compared to hand sanitizer alone (Larson et al. 2010). In contrast, several randomized trials of households limited to face mask use alone had found no reduction in influenza transmission (Aiello et al. 2010; Canini et al. 2010; Cowling et al. 2008).

Lacking clear information on the benefits of community-level face mask use,epidemiologists in early 2020 engaged in internal discussion about the potential harms and benefits of this intervention, considering aspects such as the limited existing research, the limited supply and interrupted supply chains of masks, what was known at the time about the epidemiology of SARS-CoV-2 transmission, and concerns around the potential for “risk compensation” if people who were wearing masks then engaged in fewer other preventive measures (Bamber and Christmas 2020; Brosseau 2020; Brosseau and Sietsema 2020; Cheng 2020; Javid, Weekes, and Matheson 2020; King 2020). Based on these discussions, many applied epidemiologists, including those at the World Health Organization and Centers for Disease Control, initially advised against the use of face masks by the general public. Instead, they stressed the importance of hygiene and distancing-based interventions, such as hand-washing, social distancing, and quarantine.

Over time, however, new information emerged. First, it became clear that at least some subset of Americans would be amenable to wearing masks. Second, we learned that SARS-CoV-2 could be transmitted by individuals who were not (yet) symptomatic (Gandhi, Yokoe, and Havlir 2020). Finally, as the availability and use of both fabric and surgical masks increased, it became clear that even when individuals wearing masks did increase their risk behaviors (by, for example, joining protests), the evidence did not suggest that transmission in these settings was any higher than if attendees had been unmasked (Dave et al. 2020). Together, these observations have shifted most applied epidemiologists and public health officials towards encouraging the use of face masks by all individuals (Greenhalgh et al. 2020; Roderick et al. 2020).

However, this recommendation does not mean that the academic epidemiology of face mask usage by the general public during respiratory outbreaks has necessarily advanced much beyond what we knew in January 2020, and many academic epidemiologists remain agnostic about the value of face masks. In fact, if anything, it may be fair to say that academic epidemiologists have fewer answers about the science of face masks than we did 10 months ago—simply because we now have more questions. 

Previous research on face mask usage in respiratory outbreaks focused chiefly on evaluating either N95 masks or surgical masks, both of which are subject to regulatory standards. In contrast, many of the face masks used by the general public during the COVID-19 pandemic are made from fabric, both commercially and homemade, and the filtration efficacy of these masks is both unknown and potentially highly variable (Aydin et al. 2020; Davies et al. 2013; Tcharkhtchi et al. 2020). In addition, previous studies of face mask usage typically assumed individuals had been provided with training and guidance on how to appropriately don, doff, and wear face masks to maximize their benefits. In reality, adherence both in terms of frequency and correctness of face mask use is extremely variable among the general public. Despite this, existing attempts to model the population impacts of community-level face mask use have typically assumed perfect adherence and correct usage (Ferguson et al. 2020). Academic epidemiologists likely will be investigating and debating these topics for many years to come, both to fully characterize the causal effect of community level mask-wearing strategies and to explore the actual risks and benefits that result from these (Bundgaard et al. 2020; Doung-ngern et al. 2020).

In short, the current recommendation of experts is to wear masks--even cloth masks--in many settings, not so much to protect yourself as to protect others. Lynn Peeples offers a nice readable overview of the existing evidence base in favor of wearing masks in Nature (October 6, "Face masks: what the data say.
The science supports that face coverings are saving lives during the coronavirus pandemic, and yet the debate trundles on. How much evidence is enough?" But Peeples is a fair-minded presenter of the evidence, and so she also includes statements like: 

“There’s a lot of information out there, but it’s confusing to put all the lines of evidence together,” says Angela Rasmussen, a virologist at Columbia University’s Mailman School of Public Health in New York City. “When it comes down to it, we still don’t know a lot.” ...

Human behaviour is core to how well masks work in the real world. “I don’t want someone who is infected in a crowded area being confident while wearing one of these cloth coverings,” says Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota in Minneapolis. ... For now, Osterholm, in Minnesota, wears a mask. Yet he laments the “lack of scientific rigour” that has so far been brought to the topic. “We criticize people all the time in the science world for making statements without any data,” he says. “We’re doing a lot of the same thing here.”

I wear a mask in all the recommended settings, because wearing a mask seems very likely to be better than not wearing one. But I'm also aware that countries of the European Union have recently seen a huge growth in COVID-19 cases, from well below the US level to well above it, despite widespread mask-wearing in many countries. As the WHO kept saying as it kept revising its guidance about masks, masks aren't enough---or at least certainly not the fabric or gauze masks that most of the public wear. They need to be combined with social distancing, hand-washing, self-quarantining when possibly or actually infected, and similar steps. If wearing a mask gives people a sense that they are incapable of transmitting the disease themselves or invulnerable to the disease when transmitted by others, then when the epidemiologists finish their studies of masks five or ten years down the road, they may find that the potential benefits of mask-wearing were offset when people reduced their other efforts to minimize the spread of COVID-19. 

I understand that opinions evolve. But at least in theory, public health experts have been holding conferences and publishing learned reports about pandemics for years. Wearing masks is not a high-tech intervention. It seems like the kind of issue where one might expect that public health experts have worked out a recommendation in advance, rather than making a parade of their indecisiveness--and then criticizing those who are skeptical about playing follow-the-leader as they switch recommendations.