Do face masks work? A look at more than two dozen scientific studies
Scores of studies tend to show masks’ effectiveness for COVID-19 and other diseases
ANCHORAGE, Alaska (KTUU) - As Anchorage’s mask requirement is now in effect, Alaska’s News Source has taken a look into the science that influences health recommendations and public policy, based on individual studies.
The Anchorage Assembly voted on Thursday to override Mayor Dave Bronson’s veto of the emergency ordinance requiring mask wearing that passed earlier this week. People are now required to wear masks in public spaces for no more than 60 days.
The Centers for Disease Control and Prevention and Proceedings of the National Academy of Sciences of the United States of America have done reviews of more than 150 studies on masks, determining that based on available data, masks are effective at preventing the spread of viral respiratory infections for both the person infected, and a person susceptible to infection. The organizations found that more study is needed to determine the impact of masks specifically on COVID-19.
The studies vary widely in type, scope, and even in which disease being studied. Very few major studies have been published on masks and COVID-19, and the international research community has determined that doing randomized control trials with a “control” group of unmasked participants would not be ethical.
The studies that do examine COVID-19 are in varying settings, and often have limitations to a health care setting, or single type of masks.
It’s clear in the public discourse on masks’ effectiveness, and the use of them in public settings, that many people and policymakers want a single study that answers with a definitive yes or no: Do masks work for COVID-19? But just as there are many factors into how a person and society are affected by an illness or pandemic, the effectiveness of masks, types of masks, COVID-19, and human behavior are all independent factors that have been studied at length by researchers.
Most of the studies find that mask use is effective in slowing the spread of COVID-19 and recommend universal masking.
Here’s a look at some of the studies found by both the CDC and the Proceedings of the National Academy of Sciences to be most important to making decisions on the current SARS-CoV-2 pandemic.
- One observational study of Beijing households found that mask use by all residents of a household before symptoms of COVID-19 reduced secondary transmission by 79%.
- Another study in Beijing found that people who always wore masks while going out had a 70% less risk of getting SARS, a different type of coronavirus than the one that causes COVID-19. This study did not look at the risk of the mask wearer spreading the disease.
- One medical reviewer found mixed results in studies on masks and physical interventions to reduce the spread of respiratory viruses. The reviewer found in one case that masks are “the best performing intervention across populations, settings and threats,” but in another instance that there was “insufficient evidence” to recommend masks alone, without a combination of hand hygiene and physical distancing.
- A randomized controlled trial study of influenza transmission in Germany found that transmission in a household could be reduced by non-pharmaceutical interventions like face masks and intensified hand hygiene when put into place early and diligently. “Concerns about acceptability and tolerability of the interventions should not be a reason against their recommendation” the study’s conclusion states.
- Other influenza studies found similar results, with one suggesting that non-pharmaceutical measures like face masks and hand hygiene “should be recommended in crowded settings at the start of an influenza pandemic.”
- High-level studies of countries and regions with masking mandates found that transmission was higher in areas without mask mandates. One study found that countries without a mask mandate or universal masking had transmission 7.5 times higher than countries that did.
- Last June, Goldman Sachs looked at mask mandates’ impacts on Gross Domestic Product, and found that lockdown orders would subtract nearly 5% from U.S. GDP, and that mask mandates could be a better option to reduce spread of COVID-19 and reduce the negative impacts on the economy. Their analysis found that mask mandates lower the infection growth rate by 1.3 percentage points 11-15 days after their announcement, compared to a 5.4% average growth rate before announcement. It found similar and more significant declines in the growth rate of COVID-19 fatalities up to a month later.
- A computer model showed that if 100% of the public wore face masks, the transmission rate of COVID-19 could be dropped down below 1 (meaning, the number of people on average that a sick person passes the virus to) even if masks were 50% effective with a base transmission rate (how many people one sick person infects with no mitigating measures) of 2.2, or 75% effective masks with a base transmission rate of 4.
- A computer analysis of N95 respirators and an augmented influenza variant estimated that an 80% compliance rate essentially eliminated the outbreak. The PNAS review notes that computer analyses are simplifications of the real-world, and cannot fully model all of the factors that would influence real-world results.
- Looking at how COVID-19 is transmitted, multiple studies found that high viral loads, or titers, of SARS-CoV-2 are found in the saliva of patients, and the levels are just as high in asymptomatic or presymptomatic patients as they are at their height in patients with symptoms.
- The amount of respiratory droplets expelled while speaking has also been studied at length, though the reviewers at the PNAS say the topic of aerosols or particle size, and the ability of droplets to remain suspended in the air has been confusing due to inconsistent terminology. The group standardized terminology based on droplet size for its review, and found that when speaking, a person can expel “an order of magnitude more particles” than when breathing alone.
- One study found that the smallest aerosolized particles of SARS-CoV-2 were able to reach the alveoli in a person’s lungs, and medium ones were able to deposit in the trachea and large intrathoracic airways. That study found masks to be a critical barrier.
- A study that looks at the efficacy of surgical masks for controlling seasonal coronaviruses, influenza, and rhinovirus found that the masks were effective at blocking all sizes of coronavirus particles more than all sizes of rhinovirus or small sized particles of influenza in a small sample group. The coronaviruses used in the study were NL63, OC43, 229E and HKU1, not SARS-CoV-2, but they are in the same family. The preparers of the report found it one of the most relevant studies to the current COVID-19 situation.
- A study in the 1960s and 70s looked at bacteria expelled from participants’ mouths before and after masking. While talking, unmasked subjects expelled more than 5,000 contaminants per 5 cubic feet. Cloth masked subjects expelled an average of 19 contaminants per 5 cubic feet, keeping a higher percentage of the larger contaminants inside the mask.
- A number of studies of small sample sizes of specific patients showed that masks prevented or reduced virus detection, spread, or aerosolization from influenza and cystic fibrosis patients.
- A study that looked at bacteria particles expelled by the cough of healthy volunteers found that generally available household materials filtered between 58 and 94% of the 1 micron particles, while a surgical mask filtered about 96%.
- A study using laser light scattering to detect expelled particles while speaking showed that visible particles expelled forward while a person was wearing a homemade mask made of a washcloth and rubber bands remained close to background levels, while significant levels were expelled for people speaking without a mask.
- A study on face masks with exhalation valves determined that those types of masks should not be used as “source control,” or for keeping one from spreading the disease, for COVID-19.
- Simulation studies, which often use a manikin and mechanical ventilation machines for air flow, have looked at the effectiveness of cloth masks compared to surgical masks, and are particularly used for gauging how well masks do at protecting the person wearing them. Simulation studies generally use an air flow of 30 liters per minute or higher, which is about three to six times the ventilation of a person at rest or doing light work. Many of the studies use National Institute for Occupational Safety and Health standards when evaluating masks, which includes an air flow rate of 85 liters per minute, simulating a high work rate, and particles that measure 0.3 microns, smaller than virus-carrying emissions, which means that simulation studies may underestimate the efficacy of unfitted masks compared to their practical use in the community, the PNAS reviewers note.
- A study of the aerosol filtration efficiency of common fabrics used in cloth masks found a wide range of efficacy, from 12% to 99.9%, with flow rates lower than at-rest respiration, but many of them had a filtration efficiency of 96% or more for the 0.3 micron particles, including 600-thread cotton, cotton quilt, and cotton layered with chiffon, silk or flannel. The study found that a combination of materials was more effective than each material by itself.
- The review discussed that research on aerosol exposure found that all types of mask are at least “somewhat effective at protecting the wearer.” One 2008 study on masks and respiratory infections found that “any type of general mask use is likely to decrease viral exposure and infection risk on a population level, despite imperfect fit and imperfect adherence.”
- One study of mask use in health care settings related to COVID-19 published in the summer of 2020 found that physical distancing of at least 1 meter showed a large reduction in infection, and that wearing face masks protects both health care workers and patients against infection. It found that eye protection “could” confer additional benefit. The study found that none of the interventions prevented complete protection, but offered to inform guidance in the absence of more concrete, specific data.
- The PNAS review found that one study often mentioned, is also often misinterpreted. The study compared surgical masks to cloth masks, but the surgical mask group was given two new masks per day, while the cloth group received five masks for the entire four week period, wearing the same mask all day. The “control group” in this study “used masks in compliance with existing hospital protocols.” The study suggested that cloth masks should not be recommended for health care workers, “particularly in high-risk situations.” Most of the cloth mask group were washing their own masks by hand, compared to hospital laundry. In a follow-up study, switching cloth masks to hospital laundry cut the risk in half, and there was “no significant difference in infection between (health care workers) who wore cloth masks washed in the hospital laundry compared with medical masks.” The reviewers found that the study doesn’t inform public policy regarding public mask wearing compared to the absence of masks in a community setting.
- While early writings in the medical community suggested that face shields could be a viable substitute for masks, when N95 masks were in short supply, they also found in a study that the shields have large areas for escape through the eyebrows and “downjets,” and that surgical and handmade masks also had leakage jets. It found though, that “for every breathing and coughing condition, the difference between with and without face covering is always significantly larger than the differences between any tested face covering.”
- Studies on how people respond to mandatory and voluntary mask policies found that in Germany, a mandatory policy increased compliance, and that mask wearing increased other protective behaviors. An experiment found that a voluntary policy would likely lead to insufficient compliance, would be seen as less fair and could intensify stigmatization.
- A study of mask usage by health care workers found that daylong usage of a single mask could lead to contamination on the outside of the mask. It found higher risk with mask use of more than six hours, and more than 25 patients. The study suggested specifying a maximum time of continuous use for health care workers wearing a single mask.
- The CDC has more recently published a review of mask analyses specific to COVID-19, including a well-known case in which two sick hairstylists saw 139 clients for an average of 15 minutes over eight days. None of the 67 customers who were interviewed and tested afterward developed an infection. The hair stylists and customers all universally wore masks due to the local and company requirements.
- The U.S.S. Theodore Roosevelt, a Naval aircraft carrier with 382 sailors on board, had a COVID-19 outbreak. A study of the outbreak found that the use of face coverings on board showed a 70% reduced risk of infection.
- The CDC also reviewed studies of mask-wearing and found that there are no significant adverse health affects for people wearing masks. One study among adults found that there was no statistically significant difference in either carbon dioxide or oxygen levels between people both with and without a mask, both at rest and after physical activity.
- A study of surgical and FFP2 masks found that their use during exercise was safe, but with a slight reduction in performance.
- Another found that while people wearing a face mask may feel “dyspnea”, or difficulty breathing, it has only small and often hard-to-detect physiological impacts, and that “there is currently no evidence to suggest that wearing a face mask during exercise disproportionally hinders younger or older individuals.” It suggested that some people with cardiopulmonary disease may have higher dyspnea than healthy people, which may serve as a basis for seeking an exemption from a mask regulation, but that “the benefits of decreased dyspnea will need to be weighed against the risk of contracting the SARS-CoV-2 infection.”
- At a worldwide level, a look at countries’ and regions’ implementation of mask mandates found that countries that implemented mask wearing earlier in the pandemic had lower pandemic mortality rates. It found that for 24 countries that started public mask-wearing within 20 days of the onset of their country’s outbreak, the average coronavirus-related mortality rate was 4.7 per million on Aug. 9, 2020, while 17 countries that implemented mask wearing within 30 days saw a rate of 26.6 per million by that same date. The United States’ per-capita coronavirus mortality by that date was 502 per million.
- When it comes to the economy, a Washington University in St. Louis study on the economy and social distancing found that social distancing had a large effect on reducing COVID-19 spread, and that mask mandate evidence was mixed. It also found that social distancing reduces consumer spending, but that mask mandates increase consumer spending and reduce social distancing, which in turn continues to increase spending.
The PNAS review found that, after reviewing the 141 sources, public cloth mask wearing should be adopted during a shortage of medical masks, and combined with hygiene, distancing and contact tracing strategies.
“Our review of the literature offers evidence in favor of widespread mask use as source control to reduce community transmission,” the conclusion read in part.
The body recommended that mask requirements be implemented by governments or in their absence, by organizations with public-facing services.
“Given the value of the source control principle, especially for presymptomatic people, it is not sufficient for only employees to wear masks; customers must wear masks as well,” it said.
But masks requirements should come with clear guidelines for their use and sanitation or re-use, the report said. And used alongside widespread testing, contact tracing, quarantining of infected people, hand washing, and physical distancing. It also said there should be consideration of mask distribution. The report suggests that as governments withdrew lockdowns, continuing those steps could preserve health care capacity “until a vaccine can be developed.”
Anna Frick, the state’s epidemiology research analyst, said while individual studies have differing results, the variety of types of studies and data gives a good endorsement for masks working to give protection against the spread of COVID-19, even though it may not be 100% protection.
“One of the reasons I can feel so confident in saying that masks work are because we have a lot of different kinds of data from studies that were done in a lot of different populations using different methods,” Frick said in a media call in early October. “And all of them sort of come to the same conclusion that masking is an effective way to disrupt the transmission of COVID. And the variety of evidence that we have is one of the reasons that we know the evidence is really good because seeing evidence in different shapes and different kinds really supports the idea that we’re finding the right results.”
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