How does most Coronavirus COVID-19 Transmission Occur?

Large Droplets Responsible For Most Coronavirus Spread

Wearing Mask Prevents Some Infection When Healthy

 Wearing Mask Prevents Most Spread If Sick (or + Mild Symptoms or Don’t Know)





IF YOU ARE SICK: Wear a face mask at home when moving around, near a caretaker, when going out in public or in a hospital.

IF YOU ARE NOT SICK: Wear a face mask whenever you go out in public, to a hospital or if you are caring for someone who is sick.

IF YOU ARE A HEALTH CARE WORKER OR CARETAKER FOR SICK: Wear a face mask whenever you go out in public, to a hospital or if you are caring for someone who is sick. Consider following recommendations for Sick (as above), due to possibility of infection and spreading infection before you have symptoms.

HOME MADE OR DO-IT-YOURSELF (DIY)** MASKS: May substantially reduce the spread of Corona virus.

RESERVE PROFESSIONAL MASKS FOR HEALTH CARE WORKERS: Since they need them for surgery, procedures and caring for many sick patients.

Opinions from Experts:

Respiratory Medicine & SARS Expert David Hui Says Masks Particularly Important In COVID-19

  • Patients with COVID-19 frequently have only minor symptoms
  • Some researchers believe there may be asymptomatic transmission Inconclusive evidence for masks is “not a reason to dismiss”
  • Since “can’t randomize people to not wear a mask, and some to wear a mask, and then expose them all to the virus”
  • “If you are standing in front of someone who is sick, the mask will give some protection.”
  • “The mask provides a barrier from respiratory droplets, which is predominantly how the virus spreads.”

 London Infectious Disease Expert Warns Decisions Needed Now

We need to make policy decisions and clinical decisions now…

You can’t say, ‘Let’s wait a month until we have the data…

Right now, we need to do anything that buys us one week, two weeks; anything to delay will
have a dramatic impact…[because]…If London,  Seattle or Paris goes through what northern Italy is going through at the
moment, it will be devastating.”  

-Dr. Jeremy Farrar, infectious disease specialist, director of research at Wellcome in London 2020

Why Not Recommend Masks to Public?

“If there’s a general recommendation that people wear face masks, we won’t have enough supply for healthcare workers”

“Scant evidence” & “don’t fit snugly” for members of the general public”

-Dr. William Schaffner, professor in Vanderbilt University’s Division of Infectious Diseases Time.Com 2020

Other reasons include:

  • Lack of quality assurance, regulation wide range of cloth masks or improvised masks used around the world Chughtai 2015
  • Cloth masks include cotton and gauze masks that are homemade or woven Chughtai 2015
  • Surgical masks face similar issues, unlike NIOSH certified N95 Chughtai 2015
  • Concern that cloth masks may encourage risk taking or decrease other hygiene measures due to a false sense of protection Chughtai 2015

Counter-points to Why Not Recommend Masks to Public

1. Agree supply of masks needs to be prioritized for healthcare workers. However, recommendations
for Cloth, DIY or home masks will not affect the health care worker supply

2A. No conclusive evidence exists for any medical masks. If sufficient for medical professional it’s enough to recommend to physicians & should be recommended to general public also.

2B. Even if evidence is lacking it is “not a reason to dismiss” especially when “we need to do anything” to buy us time and when any delay could “be devastating.” “You can’t say, ‘Let’s wait a month until we have the data…we need to make…decisions now”

2C. Randomized controls trials RCTs for masks “isn’t possible but because there would be serious eithical issue and problems with exposing individuals to a virus” therefore, most evidence comes from laboratory or observations studies. There are at least 19 studies on cloth masks that suggest efficacy as well as anecdotal data (see table below).

3. Snug Fit is not a major issue for barriers from large droplets and not relevant to the current guidelines as N95 is only recommended for physicians performing procedures.

4. Surgical masks used in healthcare face similar issues to cloth masks Chughtai 2015, unlike NIOSH certified N95. Though surgical masks superiority appears to ability to used in the operating room due to fluid resistance IOM 2006

5. Currently, being used successfully in countries in Asia with successful response and in the Past….

Cloth Masks Have Worked and Been Recommended by DOH & CDC During Supply Shortage

  • Non-disposable cloth masks were used to protect healthcare workers from scarlet fever, measles, influenza, plague and tuberculosis.  Mcintyre et al 2015 
  • Use continues today in developing countries like India because they last long, easy to carry, nonallergenic, comfortable, affordable, and washable.  IOM 2006 
  • During the SARS Outbreak in 2002 the public in Asia was encouraged to wear reusable gauze or cotton masks that could be washed with disinfectants or sterilized with high pressure and temperature. IOM 2006 
  • Use of masks, social distancing and hand hygiene were found be strongly protective and significantly reduced the risk for SARS IOM 2006 
  • CDC recommended using cotton masks for infection control of viral hemorrhagic fevers in the African health care setting when surgical masks are not available
  • Regional pandemic influenza plans (Sonoma County DOH in 2006) discuss the use of cloth masks in the event of a shortage of N95 and surgical masks Chughtai et al 2013
    • Implies cloth masks protect against droplet as well as against airborne particles
    • Research has shown cloth from a Hanes Sweatshirt can filter out 55% of particles in the 20-1000 nanometer range during penetration testing Shaffer et al 2010

Author Year Mask Type Main Findings
Weaver, 1918 Two layered gauze masks Low rates of diphtheria and
scarlet fever observed in HCWs after using masks
Capps, 1918 Cloth Masks The secondary transmission of
scarlet fever and measles was reduced in the wards by using masks
Haller, 1918 Gauze masks The number of colonies depends on
the type of gauze and number of layers
Doust, 1918 2-10 layer gauze/cloth Three layer butter cloth masks,
made of fine gauze, were found to be more effective in preventing spread of
Leete, 1919 Dry/wet gauze and muslin 6 to 8 layers of fine muslin
provided better protection than gauze masks. Dry masks are better than wet
Weaver, 1919 Gauze masks The number of colonies in the
petri dishes was decreased by increasing the distance of the spray from the
opening, increasing fineness and number of layers of cloth
Kellogg, 1920 Gauze masks Certain types of masks may be
effective, (depending on type of cloth and number of layers), however use
should not be compulsory. Leakage around the face increased when thin layer
of gauze used
Walker, 1930 various masks, including gauze
mask of two
Of 42 masks, only 7 masks were of
good quality. None of them was germproof in testing. Gauze mask with rubber
in the centre was considered germ proof.
Blatt, 1933

Cloth n/a, cellophane

gauze mask

Simple 6 layer gauze masks were
not effective. Newly made cellophane gauze masks were effective and
comfortable to wear.
Paine, 1935 Silk, surgical & dental gauze Two layers of silk, eight double
layers of surgical gauze and four layers of dental gauze are effective in
reducing droplet penetration. The design of mask is important
McKhann, 1938 Gauze, impervious, paper, cotton New type of filter masks were
most effective. Paper masks were not effective as they become wet very
McNett, 1949 layers of cloth masks 50% reduction in the prevalence
of TB was observed in the nurses after using 6 layer cloth masks
Lurie, 1949 3 to 6 layer of gauze masks 4 to 6 layer gauze masks
effectively filter 90 to 95 of the bacillus. Wearing masks was recommended.
Shooter, 1959 2 – 4 layer cotton, cambric, paper All masks were found effective in
preventing spread of staphylococci infection
Greene et al., 1975 2 layers of fine muslin  Masks were effective mainly against large
particles, ie  greater than 4 um
Quesnel, 1975 4 layer cotton,
polyester and
 All masks were effective against large
particles; however three of them were more effective against small particles
Dato, 2006 Cotton (heavyweight T-shirts)  Handmade masks can provide good fit and
reasonable protection
Sande, 2008 Compare Respirator, surgical mask and homemade
cloth mask
 All masks provide some protection, however
respirators provide maximum protection, followed by surgical masks and then
homemade cloth masks
Rengasamy et al, 2010 Various types of fabrics were
tested, including sweatshirts, T-shirts, towels, scarves, and cloth masks
 The respiratory protection is minimal with
cloth masks and certain types of cloth fabric may impart more protective
value than others

Chart is adapted from Chughtai 2015

Disclaimer: This is a work in progress and does not represent official medical advice or public health advice that should be relied on by any individuals at this time. If you are a patient with any questions related to medical advice or corona virus call 911. This was created for discourse related to identifying policy and procedures that may assist public health officials. For official advice related to public health and effective prevention techniques please contact your local health department or the Centers for disease control at 800-CDC-INFO (800-232-4636) or the World Health Organization at (202) 974-3000.

Please follow and like us: