Masks: How Effective Are They? An Update

Here are three pieces that are packed with research and tons of relevant footnotes and links.

Masks-for-all for COVID-19 not based on sound data.

A very good overview by Forbes.

Here are all the collected links on masks

The definitive study of masks and the 1918 Influenza

Masks have not been proved efficient enough to warrant compulsory application for the checking of epidemics, according to Dr. Kellogg, who has conducted a painstaking investigation with gauzes. This investigation is scientific in character, omitting not one of the necessary factors. It ought to settle the much argued question of masks for the public.

Should Everyone Wear A Mask In Public? Maybe—But It’s Complicated

“The question a month ago was will they protect you, the wearer, and the answer is still, they probably won’t protect you,” Eli Perencevich, the University of Iowa. One of the biggest reasons they won’t protect the average wearer is that most don’t wear them correctly—even when trained—and unconsciously engage in counterproductive behaviors, such as touching the mask frequently.

The historical peer-reviewed evidence on universal mask wearing to reduce community spread remains inconclusive. Here’s a short summary of what the peer-reviewed evidence does show, all of which must be considered through the lens of other issues discussed further down and the fact that COVID-19 is a new disease caused by a new pathogen:

  • Homemade masks were not as effective as surgical masks in preventing wearers from expelling droplets, but they did reduce droplets and were better than no protection, according to a 2013 experiment.
  • The combination of wearing a mask and hand-washing – but not either one by itself – reduced household transmission of influenza by 35-51% in a 2010 study.
  • Flu-like illnesses occurred 13 times more often in healthcare workers wearing cloth masks compared to surgical masks, and 97% of particles penetrated cloth masks, compared to 44% penetrating surgical masks, according to a 2015 study.
  • Wearing a mask decreased infection risk by 60-80% when a parent was caring directly for a sick child in the same household, but mask adherence was well below 50%, leading the authors of a 2009 study to conclude that masks were “ineffective in controlling seasonal influenza-like illness” but might work better with better adherence. Further, the authors urged “caution in extrapolating our results to school, workplace, or community contexts, or where multiple, repeated exposures may occur, such as in healthcare settings.”
  • A 2015 systematic review of nine randomized controlled trials consistently found that real-life use of medical masks overall did not reduce infections compared to no masks except in the 2009 study above when adherence was high. Five studies found small reductions in risk with a combination of mask-wearing and hand-hygiene, while the others found no benefits.
  • Five separate studies in the 2015 review above found that N95 respirators significantly reduced infections compared to surgical masks. 
  • Masks blocked live influenza particles in a 2013 simulation experiment with a dummy, but studies showing that masks block droplets or even infectious particles cannot be assumed automatically to prevent infections.
  • Wearing masks appeared to reduce SARS transmission risk, with approximately one infection prevented for every six people wearing a mask, according to a 2008 systematic review
  • Face masks were not helpful in reducing transmission of pandemic influenza, according to a 2017 systematic review and meta-analysis.

Do face masks work against the coronavirus and should you wear one?

In 2015, MacIntyre and her colleagues ran a clinical trial pitting cloth masks against medical ones. The team provided 1607 healthcare workers at 14 hospitals in Hanoi, Vietnam, with either disposable medical masks or reusable cloth ones, which could be washed at home at the end of the day they were worn. Those that wore cloth masks were significantly more likely to catch a virus, the team found.

But what about the rest of us? In an attempt to answer this question, Paul Hunter at the University of East Anglia, UK, and his colleagues looked at 31 published studies on the efficacy of face masks.

Overall, the evidence suggests there may be a small benefit to wearing some kind of face covering. They do seem to prevent sick people from spreading the virus, but the evidence is weak and inconsistent, says Hunter.

“Our view is that there was some evidence of a degree of protection, but it wasn’t great,” he says. “So we still don’t effectively know if face masks in the community work.”

Hunter thinks there is enough evidence to support mask-wearing for some frontline staff, such as those working in public transport or supermarkets, as well as vulnerable people who temporarily enter high-risk environments like hospitals – as long as their use doesn’t deprive healthcare workers of equipment.

Do face masks really reduce coronavirus spread? Experts have mixed answers.

The bottom line, experts say, is that masks might help keep people with COVID-19 from unknowingly passing along the virus. But the evidence for the efficacy of surgical or homemade masks is limited, and masks aren’t the most important protection against the coronavirus.

Report on face masks’ effectiveness for COVID-19 divides scientists

The conclusion is based on analysis of three key considerations, including the role of droplets as a route of transmission, and whether masks can help to reduce dispersal of droplets. However the authors note there are only a small number of studies.

But the report prompted other scientists to express their reservations, warning that it amounted to no more than opinion and overstated the available evidence.

Dr Antonio Lazzarino of the Department of Epidemiology and Public Health at University College London, agreed.

“That is not a piece or research. That is a non-systematic review of anecdotical and non-clinical studies,” he said.

“The evidence we need before we implement public interventions involving billions of people, must come ideally from randomised controlled trials at population level or at least from observational follow-up studies with comparison groups,” said Lazzarino noting that will allow experts to look at the pros and cons of wearing masks.

“Based on what we now know about the dynamics of transmission and the pathophysiology of Covid-19, the negative effects of wearing masks outweigh the positive,” he said.

The Effectiveness of Surgical Face Masks: What the Literature Shows

Much of the literature on masks consists of anecdotal evidence or summaries of previous studies. The rationale for wearing masks has shifted from protection of the patient to protection of the health care professional wearing the mask. Currently there is little evidence that wearing a surgical mask provides sufficient protection from all the hazards likely to be encountered in an acute health care setting: the use of a respirator and face shield should be considered depending on the circumstances.

Face masks cannot stop healthy people getting COVID-19, says WHO

The World Health Organization has held off from recommending people wear face masks in public after assessing fresh evidence that suggested the items may help to contain the pandemic.

The WHO reviewed its position on masks in light of data from Hong Kong indicating that their widespread use in the community may have reduced the spread of coronavirus in some regions.

WHO updated guidelines

Wearing a medical mask is one of the prevention measures that can limit the spread of certain respiratory viral diseases, including COVID-19. However, the use of a mask alone is insufficient to provide an adequate level of protection, and other measures should also be adopted. Whether or not masks are used, maximum compliance with hand hygiene and other IPC measures is critical to prevent human-to-human transmission of COVID-19. WHO has developed guidance on IPC strategies for home care and health care settings for use when COVID-19 is suspected.

Medical masks should be reserved for health care workers

The use of medical masks in the community may create a false sense of security, with neglect of other essential measures, such as hand hygiene practices and physical distancing, and may lead to touching the face under the masks and under the eyes, result in unnecessary costs, and take masks away from those in health care who need them most, especially when masks are in short supply.

Nonpharmaceutical Interventions for Pandemic Influenza, National and Community Measures

“Hand and respiratory hygiene should be routine; mask use should be based on setting and risk…”

Surgical, Cotton Masks Equally Ineffective in Blocking COVID-19 Spread, Say Investigators

Surgical and cotton masks are both ineffective when it comes to blocking droplets of the virus SARS–CoV-2 that may be generated when somebody coughs, according to investigators with the Ulsan College of Medicine, Seoul, South Korea. Their research letter, published yesterday in the Annals of Internal Medicine, compared the 2 types of masks. Four patients coughed 5 times each into a petri dish while wearing no mask. They then coughed five times wearing a surgical mask, a cotton mask, and then, again, wearing no mask. The study, conducted at two hospitals in Seoul, found that when patients coughed into either type of mask, droplets of SARS–CoV-2 were released into the environment.

Effectiveness of surgical masks against influenza bioaerosols

Most surgical masks are not certified for use as respiratory protective devices (RPDs). In the event of an influenza pandemic, logistical and practical implications such as storage and fit testing will restrict the use of RPDs to certain high-risk procedures that are likely to generate large amounts of infectious bioaerosols. Studies have shown that in such circumstances increased numbers of surgical masks are worn, but the protection afforded to the wearer by a surgical mask against infectious aerosols is not well understood.

Face Masks to Prevent Transmission of Influenza Virus: A Systematic Review

There are fewer data to support the use of masks or respirators to prevent becoming infected. Further studies in controlled settings and studies of natural infections in healthcare and community settings are required to better define the effectiveness of face masks and respirators in preventing influenza virus transmission.

Reusability of Facemasks During an Influenza Pandemic

No device is fail-safe, and its effectiveness depends on fit, level of exposures, and appropriate use. None of these devices protects against transmission of flu spread through direct contact, and hand washing is necessary when using and after removing these devices.

Assessing the State of Knowledge Regarding the Effectiveness of Interventions to Contain Pandemic Influenza Transmission: A Systematic Review and Narrative Synthesis

Noting important limitations in the studies reviewed, these authors suggest that masks and respirators may be cost-effective, though there is insufficient data to inform more specific interventions.

Economic Analysis of the Use of Facemasks During Pandemic (H1N1) 2009

Several laboratory studies on mask effectiveness have shown that N95 respirators are 21.5% effective in protecting against the inhalation of nanoparticles, while surgical masks were only 2.4% effective (an Lee et al., 2008). However, a study by Loeb et al. (Loeb et al., 2009) found that surgical masks and N95 respirators offered about the same percentage of protection for nurses in hospitals. Although several studies have shown that both surgical masks and N95 provide similar protection against influenza, a recent editorial by Killingley (Killingley, 2011) discusses two studies and argues that the results are still inconclusive and that more research is needed.

A cluster randomized clinical trial comparing fit‐tested and non‐fit‐tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers

The rates of CRI (3·9% versus 6·7%), ILI (0·3% versus 0·6%), laboratory‐confirmed respiratory virus (1·4% versus 2·6%) and influenza (0·3% versus 1%) infection were consistently lower for the N95 group compared to medical masks. All infection outcomes were consistently higher (approximately double) in the medical mask group compared to the N95 group (Figure 2).

Face masks to prevent transmission of influenza virus: a systematic review
There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. There are fewer data to support the use of masks or respirators to prevent becoming infected. Further studies in controlled settings and studies of natural infections in healthcare and community settings are required to better define the effectiveness of face masks and respirators in preventing influenza virus transmission.

Effectiveness of personal protective measures in reducing pandemic influenza transmission: A systematic review and meta-analysis

Meta-analyses suggest that regular hand hygiene provided a significant protective effect (OR = 0.62; 95% CI 0.52–0.73; I2 = 0%), and facemask use provided a non-significant protective effect (OR = 0.53; 95% CI 0.16–1.71; I2 = 48%) against 2009 pandemic influenza infection.

Face Mask Use and Control of Respiratory Virus Transmission in Households

We found that adherence to mask use significantly reduced the risk for ILI-associated infection, but <50% of participants wore masks most of the time. We concluded that household use of face masks is associated with low adherence and is ineffective for controlling seasonal respiratory disease. However, during a severe pandemic when use of face masks might be greater, pandemic transmission in households could be reduced.

The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence

None of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection. Some evidence suggests that mask use is best undertaken as part of a package of personal protection especially hand hygiene. The effectiveness of masks and respirators is likely linked to early, consistent and correct usage.

Looking at the evidence on homemade face masks to prevent coronavirus transmission

The past president of the Society for Healthcare Epidemiology of America, Dr. Daniel Diekema, was eager to answer some of my questions. To my surprise, he wasn’t all that enthused about their usefulness. “Maybe it could be helpful, but I just don’t think the evidence is there for it. So I’m not a huge proponent of mask use in public,” he said.

This goes against the grain, especially in California where public health officials have urged everyone to wear masks when they go outside, which some interpret as a warning that even if they are out alone, or out for a solo walk or a run, they need to wear a face mask lest they get infected when the wind blows toward them the air someone else breathed.

“If you’re going to wear a home-made mask, it should not replace physical distancing, good hand hygiene and the instructions about not touching your face, eyes, nose and mouth,” said Diekema, director of infectious diseases at University of Iowa HealthCare.

Wearing a mask is far less useful than doing those things, he said. More importantly, it could give wearers and those they come in contact with a false sense of security, as if the mask is going to be their salvation.

Effectiveness of Surgical and Cotton Masks in Blocking SARS–CoV-2: A Controlled Comparison in 4 Patients

Face Masks: Much More Than You Wanted To Know

But the CDC has recommended against mask use. I hypothesized that the CDC was intentionally lying to us, trying to trick us into not buying masks so there would be enough for health care workers.

But that can’t be true, because the CDC and other experts came up with their no-masks policy years ago, long before there was any supply shortage. For example, during the 2009 swine flu pandemic, their website offered the following table:

Table 1. CDC Interim Recommendations for Facemask and Respirator Use for Home, Community, and Occupational Settings for Non-Ill Persons to Prevent Infection with 2009 H1N1 1 2
Setting Persons not at increased risk of severe illness from influenza
(Non-high risk persons)
Persons at increased risk of severe illness from influenza (High-Risk Persons) 3
No 2009 H1N1 in community Facemask/respirator not recommended Facemask/respirator not recommended
2009 H1N1 in community: not crowded setting Facemask/respirator not recommended Facemask/respirator not recommended
2009 H1N1 in community: crowded setting Facemask/respirator not recommended Avoid setting.
If unavoidable, consider facemask or respirator 4 5
Caregiver to person with influenza-like illness Facemask/respirator not recommended Avoid being caregiver. If unavoidable, use facemask or respirator 4 5
Other household members in home Facemask/respirator not recommended Facemask/respirator not recommended
Occupational (non-health care)
No 2009 H1N1 in community Facemask/respirator not recommended Facemask/respirator not recommended
2009 H1N1 in community Facemask/respirator not recommended but could be considered under certain circumstances 4 5 Facemask/respirator not recommended but could be considered under certain circumstances 4 5
Occupational (health care) 6
Caring 7 for persons with known, probable or suspected 2009 H1N1 or influenza-like illness Respirator Consider temporary reassignment. Respirator
  1. The effectiveness of respirators and facemasks in preventing transmission of 2009 H1N1 (or seasonal influenza) in various settings is not known. Use of a facemask or respirator is likely to be of most benefit if used correctly and consistently when exposed to an ill person.  (Ref. a) MacIntyre CR, et al.  EID 2009;15:233-41. b) Cowling BJ, et al. Non-pharmaceutical interventions to prevent household transmission of influenza. The 8th Asia Pacific Congress of Medical Virology, Hong Kong, 26-28 February 2009.)

  2. For the purpose of this document, respirator refers to N95 or any other NIOSH-certified filtering face piece respirator.

  3. Persons at increased risk of severe illness from influenza (i.e. high-risk persons) include those groups at higher risk for severe illness from seasonal influenza, including:  children younger than 5 years old;  persons aged 65 years or older;  children and adolescents (younger than 18 years) who are receiving long-term aspirin therapy and who might be at risk for experiencing Reye syndrome after influenza virus infection;  pregnant women;  adults and children who have pulmonary, including asthma, cardiovascular, hepatic, hematological, neurologic, neuromuscular, or metabolic disorders, such as diabetes; adults and children who have immunosuppression (including immunosuppression caused by medications or by HIV); and, residents of nursing homes and other chronic-care facilities.

  4. The optimal use of respirators requires fit testing, training and medical clearance. Proper use is recommended to maximize effectiveness. The use of facemasks may be considered as an alternative to respirators, although they are not as effective as respirators in preventing inhalation of small particles, which is one potential route of influenza transmission.  There is limited evidence available to suggest that use of a respirator without fit-testing may still provide better protection than a facemask against inhalation of small particles. Respirators are not recommended for children or persons who have facial hair (see FDA website).

  5. Use of N95 respirators or facemasks generally is not recommended for workers in non-healthcare occupational settings for general work activities.  For specific work activities that involve contact with people who have influenza-like illness (ILI) (fever plus at least either cough or sore throat and possibly other symptoms like runny nose, body aches, headaches, chills, fatigue, vomiting and diarrhea), such as escorting a person with ILI, interviewing a person with ILI, providing assistance to an individual with ILI, the following are recommended: a) workers should try to maintain a distance of 6 feet or more from the person with ILI; b) workers should keep their interactions with the ill person as brief as possible; c) the ill person should be asked to follow good cough etiquette and hand hygiene and to wear a facemask, if able, and one is available; d) workers at increased risk of severe illness from influenza infection (see footnote 3) should avoid people with ILI (possibly by temporary reassignment); and, e) where workers cannot avoid close contact with persons with ILI, some workers may choose to wear a facemask or N95 respirator on a voluntary basis  (See footnote 1). When respirators are used on a voluntary basis in an occupational work setting, requirements for voluntary use of respirators in work sites can be found on the OSHA website.

  6. See case definitions of confirmed, probable, and suspected 2009 influenza A (H1N1). Also see infection control in the health care setting. When respiratory protection is required in an occupational setting, respirators must be used in the context of a comprehensive respiratory protection program as required under OSHA’s Respiratory Protection standard (29 CFR 1910.134). This includes fit testing, medical evaluation and training of the worker.

  7. “Caring” includes all activities that bring a worker into proximity to a patient with known, probable, or suspected 2009 H1N1 or ILI, including both providing direct medical care and support activities like delivering a meal tray or cleaning a patient’s room.

Should everyone be wearing face masks? It’s complicated

Should members of the public be wearing face masks during the COVID-19 pandemic? It’s a controversial question, with different countries and authorities giving different advice.

We have reviewed the results of more than a dozen randomised trials of facemasks and transmission of respiratory illnesses. We found the current best evidence suggests wearing a mask to avoid viral respiratory infections such as COVID-19 offers minimal protection, if any.

On the magical powers of masks – Snopes

Is This COVID-19 Mask Efficacy Chart Accurate?

The CDC recommends wearing a cloth face mask in public during the COVID-19 pandemic to help slow the spread of the disease.

September 2022
Free Speech Union

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