October 2020

Studies Show Masks, Gaiters Work to Prevent Spread of Coronavirus

Figure 1. Schematic of the experimental setup. A laser beam is expanded vertically by a cylindrical lens and shined through slits in the enclosure. The camera is located at the back of the box, with a hole for the speaker in the front. The inset shows scattering for water particles from a spray bottle with the front of the box removed. Photo credit: Martin Fischer, Duke University.

Since the spring, it has been demonstrated that masks are a critical deterrent to the spread of SARS-CoV-2, the virus that leads to COVID-19, the worldwide pandemic that has claimed more than 240,000 American lives, and more than 1.25 million lives globally.

Experts are agreed now that transmission of the virus is predominately by respiratory droplets when people sneeze, sing, talk, or breathe. Other transmission routes remain under investigation, but preventing airborne transmission is a key factor in the national fight to stop the spread of this potentially devastating disease.

Some have argued for allowing unchecked spread of the virus to create so-called herd immunity. The consensus of the vast majority of both public health and medical experts, however, is that the spread needs to be contained to prevent not only unnecessary deaths, but the collapse of the overall healthcare system as hospitals are overrun with COVID-19 patients forcing a rationing of care and a disproportionate number of healthcare workers are lost due to ever-increasing viral exposures.

As winter approaches and the population moves indoor, spread has already begun increasing again, with record-breaking numbers of infections, sky-rocketing positivity rates, increasing hospitalizations and ventilator usage, and ultimately, deaths. Returning the focus to basic infectious disease hygiene measures—mask wearing and routine hand-washing—will be critical.

Many have questioned the validity of mask use. Now, 2 different studies using the same protocol for testing have demonstrated that both masks and gaiters provide a level of protection against the spread of the coronavirus 19. The studies, out of Duke University (Durham, NC) and University of Georgia (Athens, GA), used the same protocol, which was developed by Martin C. Fischer, PhD, and Eric Westman, MD, both from Duke.

Masks Reduce Droplet Transference

Figure 2. Pictures of face masks under investigation. We tested 14 different face masks or mask alternatives and one mask material. Photo credit: Emma Fischer, Duke University. For photos showing the masks as actually worn, see fig. S8 (Supplementary Materials).

The proof-of-concept protocol, which was published in Science Advances, reported that a simple, low-cost technique provided visual proof that face masks are effective in reducing droplet emissions during normal wear. The setup, which was designed by Fischer, uses a box, a laser, a lens and a cell phone camera (Figure 1). Then they had a volunteer wear a face mask and speak in the direction of the boxed laser light beam. The droplets that propagate through the laser beam scatter light, which is then recorded with a cell phone camera. A computer algorithm was used to count the droplets in the 40-second videos. Their goal was to create a testing set-up that could be easily built and operated by nonexperts.

They tested 14 commonly available masks/mask alternatives as well as swaths of material and a medical-grade N95 mask (Figure 2). Four volunteers repeated the phrase “Stay healthy, people” 10 times using various masks. Droplet transmission ranged from below 0.1% with the fitted N95 mask to 110% with the neck gaiter (Figure 3).

“In the case of speaking through a mask,” they wrote, “there is a physical barrier, which results in a reduction of transmitted droplets and a significant delay between speaking and detecting particles. In effect, the mask acts as a temporal low-pass filter, smoothens the droplet rate over time, and reduces the overall transmission.”

In a subsequent news release, Fischer commented, “We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing. We could also see that some face coverings performed much better than others in blocking expelled particles.”

Notably, the researchers report, the best face coverings were N95 masks without valves – the hospital-grade coverings that are used by front-line health care workers. Surgical or polypropylene masks also performed well. And hand-made cotton face coverings provided good coverage, eliminating a substantial amount of the spray from normal speech.

Their findings for gaiters, which are often preferred by those who are physically active, were disappointing: “We noticed that speaking through some masks (particularly the neck gaiter) seemed to disperse the largest droplets into a multitude of smaller droplets, which explains the apparent increase in droplet count relative to no mask in that case. Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive.”

Gaiters Reduce Droplet Transference

Enter Suraj Sharma, PhD, and Tho Nguyen, PhD, from University of Georgia. Along with their PhD students, they used the Duke protocol to demonstrate that neck gaiters can provide a level of protection equivalent to masks when used as a face-covering.2

Materials tested consisted of the following:

  • 4 of the top-selling, 2-layer face masks offered on Amazon.com.
    • To qualify, masks had to receive no less than 2,000 consumer reviews with an average rating in excess of 4
    • Masks were made of various materials (cotton and spandex)
  • Five of the top-selling, single-layer gaiters offered on Amazon.com
    • To qualify, gaiters had to receive no less than 4,000 consumer reviews with an average rating in excess of 4.
    • Gaiters were made of various materials (polyester, spandex and nylon)
  • 3 multi-layer gaiters offered on Mission.com
    • Gaiters were 2 and 3 layers, made of polyester and spandex

Their study results showed that:

  • Single-layer gaiters provided a 77% average reduction in respiratory droplets compared to wearing no face covering at all.
  • Two-layer masks provided an 81% average reduction in respiratory droplets compared to wearing no face covering at all.
  • Multi-layer gaiters provided a 96% average reduction in respiratory droplets compared to wearing no face covering at all.

While the UGA study mirrored the protocol recently developed by Duke University, these researchers added enhancements for more accurate results.

Figure 3. Droplet transmission through face masks. (A) Relative droplet transmission through the corresponding mask. Each solid data point represents the mean and SD over 10 trials for the same mask, normalized to the control trial (no mask), and tested by one speaker. Hollow data points are the mean and SDs of the relative counts over four speakers. A plot with a logarithmic scale is shown in fig. S1. The numbers on the x-axis labels correspond to the mask numbers in Fig. 2 and Table 1. (B) The time evolution of the droplet count (left axis) is shown for representative examples, marked with the corresponding color in (A): no mask (green), bandana (red), cotton mask (orange), and surgical (blue, not visible on this scale). The cumulative droplet count for these cases is also shown (right axis). t, time.

Fig. 4. Light scattering properties. (A) Angle distribution (scattering phase func- tion) for light scattered by a water droplet of 5 m diameter for illumination with green laser light. Note the logarithmic radial scale. 0° is the forward direction, and 180° is the backward direction. The camera records at around 90°, indicated by the green segment (not to scale). (B) Calculated number of photons recorded by the camera in one frame as a function of the droplet diameter. The red shaded area and the two solid lines indicate the detection thresholds of the camera. For ideal conditions (all photons impinge on a single pixel), the camera requires at least about 75 photons per frame corresponding to a droplet diameter of 0.1 m; for photons distributed over multiple pixels, the threshold is around 960 photons and corresponds to a diameter of 0.5 m.

Subjects spoke “Stay Healthy People” 5 times into each of the materials for consistency, and droplets were monitored over a 40-second period. A computer algorithm calculated the number of remaining respiratory droplets over time to determine the efficacy of each material’s ability to reduce respiratory droplets from the baseline of “no mask.” Each material was tested 3 times to increase accuracy and statistical significance.

Results were calculated using the droplet levels at both the 30-second and 40-second marks.  Enhancements to the original study were also put in place. Instead of using a HEPA-filter, UGA scientists used a class 1000 clean room as well as a 3D printed box to dramatically diminish existing particles in the air, thereby reducing the amount of “noise” or unwanted particles from appearing in the results. MISSION, a leading provider of textile accessories, provided the funding necessary to conduct the study.

“Per CDC guidelines, using face covers to prevent the spread of COVID-19 is of the utmost importance,” Sharma said. “However, recent media reports have questioned the effectiveness of gaiters as face covers. We hope this study will provide valuable evidence and insight to help answer those questions. In sum, the level of protection provided by a face covering appears to be substantially driven by the number and quality of layers of material and not whether it’s in the form of a gaiter or a mask.”

  1. Fischer EP, Fischer MC, Grass D, Henrion I, Warren WS, Westman E. Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Sci Adv. 2020;6(36):eabd3083.
  2. Powell C. Study finds neck gaiters can reduce droplet spread. Press Release. Available at https://www.fcs.uga.edu/news/story/study-finds-neck-gaiters-can-reduce-droplet-spread . Accessed 10/20/2020.

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