Our team strives to keep up with the latest research in order to continuously inform our approach. Context and analysis can be helpful in interpreting and understanding the study findings. Below, we have a compiled a selection of such research.
Tags: #maskmaterial, #physicaldistance, #universalmasking, #demographics, #aerosolization
“A cluster randomized trial of cloth masks compared with medical masks in healthcare workers”, published 2015 in Infectious Diseases: https://bmjopen.bmj.com/content/5/4/e006577
This study compared respiratory infection rates of healthcare workers under different mask-wearing policies in Vietnam. One group of workers wore a single relatively loose-weave cloth mask for a whole shift, one group wore a single surgical mask for a whole shift, and one group did their normal practice, which was to wear a medical mask with patients who were coughing or sneezing. The study found that healthcare workers wearing medical masks were better protected than those wearing cloth masks. It’s important to notice that the cloth masks in this study had a relatively loose weave, and none of the patients wore masks. Other studies have shown that the fabric weave matters a lot, and that masks are more likely to prevent disease transmission when they are worn by sick people rather than healthy people.
“Testing the efficacy of homemade masks: Would they protect in an influenza epidemic?” Published in 2013 in Disaster Medicine and Public Health Preparedness.
Expecting the possibility of a mask shortage in a global pandemic, the researchers tested how effective a variety of household fabrics would be as masks. They balanced filtration capability against breathability. Vacuum bags and multiple layers of tea towels were the most effective filters, but they were difficult or impossible to breathe through. The authors suggest using tightly woven cotton and cotton t-shirts, which balance filtration against breathability. According to their tests, cotton t-shirt or tight-woven cotton was 65% as effective at filtering as a surgical mask.
“On coughing and airborne droplet transmission to humans,” published in 2020 in Physics of Fluids.
A group of physicists performed a very detailed simulation of a mild human cough at room temperature with different levels of wind to track how far droplets might travel. With no wind, all droplets fell to the ground within 2 meters (6 feet). However, in their slowest wind condition (4 km/h), they found that the droplet cloud from the cough could travel as far as 6m and remain relatively intact. The cough cloud also remained relatively intact for several meters in higher wind conditions (15 km/h) but dispersed substantially by 6 m. This study indicates that maintaining a 2 m separation a symptomatic person may not guarantee safety from infection, but there are still many unanswered questions. One important question is whether the droplet cloud disperses more quickly with many short gusts of wind from different directions, which is more similar to outdoor conditions. This study supports limiting time indoors in areas with relatively controlled airflow, and additional physical distancing measures like masking.
“Association between universal masking in a health care system and SARS-CoV-2 positivity among health care workers,” published in 2020 in Journal of the American Medical Association.
Original research article:
Editorial by CDC spokesperson & director:
Article in Wall Street Journal:
Mass General Brigham implemented a universal masking policy in March, requiring all health care workers, patients, and visitors to wear a mask. A group of researchers compared healthcare workers’ infection rates before universal masking, during a transition period when universal masking had been implemented but people who were already infected were likely to show symptoms, and during the intervention period, when everyone in the hospital system was required to wear a mask. The infection rate dropped significantly when everyone in the hospital system wore a mask.
“Developing home-disinfection and filtration efficiency improvement methods for N95 respirators and surgical facial masks: stretching supplies and better protection during the ongoing COVID-19 Pandemic,” published in 2020 in Journal of the International Society for Respiratory Protection.
Plain language blog entry by the authors describing their results: https://blogs.ei.columbia.edu/2020/04/21/coronavirus-disinfect-mask-home/
This group of researchers tested two things: First, how well N95, surgical, and cloth masks made of some common materials could filter particles in the size range of SARS-CoV-2 after repeated sterilization; and second, how to improve mask fit. In the repeated sterilization tests, they found that heating in an oven at 77C (170F) for 45 minutes did not harm any of the masks’ ability to filter, although one of the brands of N95 masks suffered damaged nose pads. To improve fit, they used heat-molded custom-fit plastic nose pieces. A surgical mask with no nose piece filtered about 42%, while a surgical mask with a custom nose piece filtered 88% of particles -- almost as good as an N95. They reported a filtration rate of 55% without a nose piece for cloth masks, which was better than the surgical masks but was not improved with a nose piece. However, it is important to note that they collapsed their “cloth masks” across three different materials: cotton sweaters, tight-woven cotton dress material, and polyester scarves. Their tests of each individual mask material indicate that the cotton dresses filtered about 70% of particles without a nose wire.
“Is it safe to make a DIY mask out of a vacuum bag? Debate erupts”
Experts agree that any mask made from a fiberglass filter, such as a HEPA filter, is unsafe. Some vacuum manufacturers have released statements that their bags do not contain fiberglass, but do not claim their bags are safe to breathe through. ShopVac released a statement explicitly telling customers not to use their vacuum bags as filters. Given that breathing through vacuum filters is extremely difficult and we do not know how safe it is to breathe through them at all, it is best not to make your homemade masks out of them.
“Fiberglass,” posted by the Washington State Department of Health.
HEPA filters are made of fiberglass, and this page describes the health effects of handling fiberglass. Filters made of fiberglass occasionally shed small fibers, which can cut and irritate your nose, throat, and lungs. Cutting fiberglass creates much more of this dangerous shed. HEPA filters should absolutely not be used to make masks.
“‘Only those with plastic visors were infected’: Swiss government warns against face shields.”
This is not a scientific study, but an article about an outbreak at a hotel in Switzerland. The hotel allowed staff to wear either a face mask or a face shield. A small outbreak occurred at the hotel, and “several” employees were infected along with one guest. The infected staff had all opted to wear face shields instead of masks, and the guest had been in contact with a staff member wearing a shield. We don’t know the actual number of staff members infected or how many staff opted to wear face masks versus face shields, so it is difficult to draw conclusions from the evidence in this article alone. However, if we err on the side of caution, it is better to assume that face shields are insufficient protection and face masks are much more effective.
“Hairstylists with COVID-19 didn’t infect any of their 139 clients. Face masks may be why.”
This is a news article about an incident in Missouri where two hairstylists served 139 clients while contagious with COVID-19. Both stylists and all of the customers reported wearing either surgical or double-layered tight-woven cotton masks during the whole encounter, and none of the clients or coworkers who interacted with the stylists reported infection. This was not a controlled scientific study, but the large number of client interactions up close and indoors without COVID-19 transmission suggests that universal masking may provide a measure of protection against infection.
“Contact tracing during coronavirus disease outbreak, South Korea, 2020,” published in 2020 in Emerging Infectious Diseases.
The government in South Korea tracked infected people and their contacts to determine how quickly and easily the disease spread. A group of researchers analyzed this data, taking into account the ages of the infected people and whether the contacts being traced shared a home with the infected person or not. They found that older people were more likely to infect people outside their household than younger people: about 4.7% of people who came in contact with someone over the age of 70 would develop symptoms of the coronavirus, compared with about 1.9% of people who came in contact with someone between 40 and 60 or 1% of people who came in contact with someone under 19 years of age. Young children under the age of 9 and young adults aged 20-29 were the least likely to infect someone in their own household: 5.3% of people sharing a household with a sick child later tested positive for COVID-19 (7% for young adults). Infection rates climbed with age for adults older than 30. The researchers did not control for the size of a family or its members, so it’s possible that young adults were less likely to infect household members because they lived alone, had smaller households without children, or had a young child who was less likely to become sick.
“SARS-CoV-2 Reverse Genetics Reveals a Variable Infection Gradient in the Respiratory Tract,” published in 2020 in Cell
Original study: https://www.cell.com/cell/fulltext/S0092-8674(20)30675-9
A group of geneticists looked at the types of cells in different parts of the respiratory system (nose, throat, lungs) to figure out what parts of it were most susceptible to the novel coronavirus. They found that the type of cells most likely to both become infected and shed the virus are commonly found in the nose. This means that it is very important to make sure that your mask stays over your nose.
“Dr. Anthony Fauci: To keep churches safe, use masks, limit singing and wait to resume Communion,” published in America Magazine in 2020
Dr. Fauci recommends that church services should be socially distanced, meaning parishioners should not take communion and should have limited attendance so that people do not have to sit next to each other in the pews. Do not sing, since singing releases more small droplets that can travel farther into the air.
Tags: #physicaldistance, #aerosolization
“High COVID-19 Attack Rate Among Attendees at Events at a Church — Arkansas, March 2020,” report from the CDC, 2020
Two asymptomatic people infected at least 35/92 parishioners during church events over a single weekend. Most of those infected were under the age of 65. The 35 infected people infected an additional 26 -- a much lower infection rate than at the church events.
“High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020,” report from the CDC, 2020
An asymptomatic person infected 32/60 fellow choir members during a single 2.5-hour choir practice. Those in the practice stood within 6 feet of each other, and transmission rates were likely augmented by the act of singing.
Tags: #physicaldistance, #aerosolization
“Is Singing in a Choir Safe During COVID-19? A Voice Expert Explains the Risk,” interview conducted by Massachusetts Eye and Ear, 2020
The director of the Division of Laryngology at Mass. Eye and Ear answers questions about singing and aerosolization. Singing is more dangerous than talking or even coughing because singers are “diaphragmatic athletes” who recruit air from more areas of their lungs and project it further. The smallest areas of the lungs produce the smallest particles, which are most likely to remain in the air for longer and therefore travel the furthest distances. The doctor says that there is no way to safely sing in groups for the time being.
“It is Time to Address Airborne Transmission of COVID-19,” published in Clinical Infectious Diseases, 2020
Original letter: https://academic.oup.com/cid/article/doi/10.1093/cid/ciaa939/5867798
Plain language news feature: https://www.nature.com/articles/d41586-020-02058-1
A group of doctors and scientists signed a letter saying that there is evidence people can be infected by aerosols released during talking and exhaling. They advocate for public safety measures that assume COVID-19 can be caught from these aerosols and tiny microdroplets that can stay airborne long enough to infect people well beyond the typical 1-2m accepted “safe” distance from an infected person. The doctors are particularly concerned about indoor transmission where air is recycled, still, or moved in streams by an air conditioner. Specifically, they suggest that people spend time outdoors rather than indoors, circulate outdoor air as often as possible through indoor spaces, and use high-efficiency filtration and germicidal measures to clean recirculating air when necessary. They also warn against over-crowding, especially indoors.
“Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy,” published in Environmental Research, 2020
Humans produce aerosols when we talk, exhale, and cough. Aerosols are often less infectious than large droplets because they contain less virus -- possibly not enough to cause infection at all. We do not yet know how many virus particles are required for a new infection, but there is some evidence that COVID-19 has been transmitted by aerosol. An infected person wearing a mask transmits significantly fewer aerosols, and a susceptible host wearing a mask filters out about a quarter of the aerosols, reducing the viral load and thus reducing the likelihood of infection.
Tags: #aerosolization, universalmasking
“Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1,” published in New England Journal of Medicine, 2020
The virus which causes COVID-19 can be detected on surfaces after three days. Hard and non-porous surfaces like plastic and steel had the lowest rates of degradation. Aerosols containing the virus contain detectable virus particles after three hours. However, the degradation was not tracked after the three days or three hours, so we don’t know how long it actually remains detectable -- just that it’s more than three days on plastic, and more than three hours in aerosols.
Tags: #aerosolization, #physicaldistance
“Aerosol emission and superemission during human speech increase with voice loudness,” published in Nature, 2020
Aerosols are not only released when someone coughs or sneezes, but also when they speak. Aerosols are particularly dangerous because, as small particles, they float longer in the air, meaning that they can travel farther, and are breathed deeper into the lungs. These scientists had people speak into a tunnel in different languages and at different volumes, and measured the sizes of droplets and aerosols that they released. Speaking louder releases more aerosols than speaking quietly, regardless of the language. There are also some people who emit more aerosols than others and it’s unclear why.
“Could SARS-CoV-2 be transmitted via speech droplets?” posted on medRxiv in 2020.
Speech generates large amounts of aerosols, which could contain infectious levels of virus. A damp cloth mask significantly reduced the number of droplets produced.
Tags: #aerosolization, #universalmasking
“Safer Singing During the SARS-CoV-2 Pandemic: What We Know and What We Don't,” published in Journal of Voice, 2020.
The authors review research on singing, aerosolization, and COVID-19 transmission to make safety recommendations to singers. Virus exhaled in the breath of asymptomatic people seems to be a driver of infection, and the virus is known to remain viable in aerosolized form for hours. Aerosols and droplets are both produced by exhaling, coughing, sneezing, and vocalizing -- whether by talking, yelling, or singing. More airflow produces more particles, so breathy singing produces more aerosols than singing with a resonant voice. However, all singing styles produce more aerosols than breathing. Outdoor ventilation is better than mechanical ventilation, but the minimum level of safe ventilation is unclear. Since cloth masks reduce aerosol and droplet transmission, everyone should wear a mask. And since aerosols can infect through the eyes, singers or audience members of singers should wear eye protection as well. They suggest that singers rehearse outside; sing with face masks; rehearse alone, remotely, or in groups of only a few people at least six feet apart; and shorten rehearsal times, on top of maintaining social distance measures, screening for symptoms, and washing all hands and shared surfaces routinely. Overall, while this review gives a series of recommendations for how to mitigate risks, each potential mitigation is couched in a warning that we do not know how much the risk is reduced. The authors reiterate that these measures may reduce risk but they do not eliminate it.