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How to Best Protect Yourself Against Covid-19:
A Scientific Approach

Date of report: 4/3/2020


     This report explains how to protect yourself against getting covid-19 if no one in your household is currently infected. It applies to those locations in the United States where the concentration of coronavirus is sufficient to require inhabitants to stay in their homes and apartments, only leaving for essential reasons; However, the information below can still be useful for others not meeting these criteria. We use science, reasoning and published information to address how to best protect yourself from covid-19. Important to this report is the understanding of how the coronavirus is transferred from an infected individual to a healthy person. With this understanding, the steps one needs to protect oneself will make logical sense.

“Your mindset should be that the coronavirus is like a powder
that can be anywhere where people have been,
that it can get on you and anything you might buy or bring into your home
but the powder will evaporate in 4 days and is not dangerous
as long as it does not get in your eyes, nose or mouth. ”

Person to Person Transmission

     Although we explained the transmission process in Section 2 of our report on The Use of Masks to Fight Covid-19, we repeat the discussion here for completeness.
(1) The Generation of Viral Matter
When a person with covid-19 sneezes or coughs, droplets are sent into the air. The heavier droplets can travel up to 6 feet before falling onto surfaces, where they can remain for up to three days depending of the type of surface (the coronavirus is fragile and disintegrates in less than four days). The finer droplets remained suspended in air as aerosols. An infected person also generates coronaviral aerosol simply while exhaling.
(2) The Transfer of Viral Matter to a Healthy Individual
A healthy person can get infected by covid-19 through three main methods:
     (i) By being hit directly by viral material when a person infected with covid-19 coughs or sneezes,
     (ii) By touching a surface with viral matter with one's hand and subsequently touching the mouth, nose or eyes, or
     (iii) By breathing aerosols containing the virus.

How to Best Protect Yourself

     Since no one in your household has the virus, your most likely chance of getting covid-19 is when you leave your home to perform essential duties. When you are in public places,

1. Do not get within 6 feet of anyone outside your household.
     This prevents transmission by method (i).

2. Do not touch your face with your hands.
     This prevents transmission by method (ii).
     Because it is difficult to get in the habit of not touching one's face, also do not touch your face at home; have a tissue of handkerchief nearby and use it instead, or, if you can wait, wash your hands with soap for 20 seconds before touching an eye, the nose or the mouth.

3. After leaving a frequented place, such as a grocery store, a gas station, etc., if possible, wash your hands as soon as possible with soap for 20 seconds or use a hand sanitizer with at least 60% alcohol content.

4. When you return home, wash your hands with soap for 20 seconds.

5. Wash your hands with soap for 20 seconds after touching any objects that come from outside into your home including packaging for the next three days.
     There is one exception to this rule: Always wash your hands after handling items from the refrigerator because viruses can survive considerably longer there.
     Steps 3-5 prevent transmission by method (ii).

6. Wear a mask.
     This prevents transmission by (i) and can help against transmission by (iii).

7. When you arrive home, remove the outer layer of your clothes and do not wear them inside your home. (You might want to set them aside for when you go out again.)
     This helps prevent transmission by method (ii).

8. In an area with a very high density of cases (such as New York City) for a person of high death risk (older, smoker, an individual with health or lung issues), it is best to wear protective eyewear when shopping in populated stores: Airtight swim goggles and swim masks provide 100% protection; next in effectiveness is almost airtight eyewear such as workman safety goggles. Even ordinary glasses offer a benefit. If desperate, use clear saran wrap entirely around the upper head to cover the eyes or glasses.
     This helps with transmission by method (i).

     Items 1-6 are contained in the current recommendations of the Center for Disease Control (CDC). For the protection of others, the CDC also recommends that when you cough or sneeze, do so into a tissue, handkerchief or the elbow region of your clothes. However, if you are wearing a mask (item 6), you will automatically be helping to protect others when you cough or sneeze by limiting your production of viral matter if you happen to have covid-19 and do not know because you are asymptomatic.

9. The CDC also recommends cleaning and disinfecting frequently touched surfaces in the home.
     It is most important to treat those surfaces that come in contact with objects and items that come from the outside into your home and surfaces that you touch after returning home. This could include, for example, the countertops on which you placed food items after going to a grocery. It includes the door handles you touch when entering your home.

     By the way, wearing gloves does not provide any additional protection against covid-19 since it is not transmitted through the skin. If you touch your face with a glove, it is the same as your hand. When returning to home from a public place, washing hands with soap effectively removes the virus from the hands. If you wear gloves and take them off, the virus can still be transferred to your hands in the process – hence it is necessary to wash your hands whether you wear gloves or not and when you wear gloves you need to dispose of them or not reuse them for three days.

An Example: Going Food Shopping and the Mindset You Should Have

     You have decided that it is necessary to go food shopping. You put on your mask using the procedure listed below and you put on the clothes that you have set aside for out-of-the-home excursions.
     Your mindset should be that the coronavirus is like a powder that can be anywhere where people have been, that it can get on you and anything you might buy or bring into your home but that the powder will evaporate in 4 days and is not dangerous as long as it does not get in your eyes, nose or mouth.
     When you enter the grocery store, you might want to clean the shopping cart handle with a sanitary wipe if you have one or spray it with a disinfectant. Proceed with your shopping, maintaining as best you can a distance of 6 feet from everyone. Do not assume that you can get closer to others because you wear a mask. You should imagine that there is a possibility that someone could have coughed or sneezed in every location of the store. Hence, you might be touching viral matter through the entire shopping process. Do not touch your face (in this case the upper face since the mask covers the lower face) with your hands! (It is useful to keep a tissue or handkerchief in a pocket just in case an urge arises to touch your face or eyes.) After checking out, going to your car and unloading the bags, use hand sanitizer if you have it.
     When you arrive home, bring the bags of groceries inside. You could have viral matter on your clothes, mask, hands, packaging and food items. Remove the outer layer of clothes and set them aside. Wash your hands for 20 seconds with soap. Take off your mask using the procedure given below (which includes washing with soap your hands for 20 seconds as one of the final steps). Put away the food. Throw away bags or set them (if they are reusable) somewhere where they will not be touched for the next three days. Because you have just touched objects that could have had viral matter on them after entering your home, wash your hands again with soap for 20 seconds. For the next three days, wash any fresh food thoroughly. As for food in cans, boxes or plastic, the food inside is safe; after removing the food from its container and after disposing of the container, simply wash your hands with soap for 20 seconds for the next three days (and always for items coming from the refrigerator). Finally, disinfect the door handles where you just entered your home and any surfaces such as countertops on which you placed food items. During this whole process, do not touch your face with your hands! If you imagine where viral matter might be and the preventive steps described in this and the previous paragraphs, you will realize that there is little chance for transmission by method (ii). You do not need to be paranoid about the possibility of having viral matter on your clothes, hands and food because if you understand what is going on, you have essentially thwarted the possibility of having covid-19 enter your body through your nose, eyes, or mouth.

     If you receive mail, you should imagine the possibility that someone might have coughed on it. After reading your mail and throwing away the unwanted parts, wash your hands with soap for 20 seconds. Disinfect any surfaces that come in contact with the mail. If in the next three days you need to touch mail items, wash your hands afterward. After three days, you can handle such items safely. If you receive a shipment in a box, use the same procedure with the box. No precautions are needed for the contents inside the box.
     When shopping for food, buy in bulk for two reasons: Firstly, you reduce the number of outside trips thereby reducing your risk of getting covid-19, and secondly, if everyone does this then the density of people in grocery stores will be less. If your outings are spaced more than three days apart, potentially virally infected items such as your mask, reusable shopping bags and “out-of-the-house-excursion clothes” will no longer have covid-19 on them, which is of some advantage.

On the Use of Masks

Proper Mask Procedures

Putting on a Mask: First, wash your hands with soap for 20 seconds. Place the mask so that it covers the nose and mouth. If it contains a metal nose pin, pinch it to help reduce air gaps near the nose region. Use tape (masking tape works fine) to seal any air gaps in the region where the masks meets the face to make it airtight. For flexible masks, you can tell if a mask is airtight because it will collapse somewhat when breathing in. The mask should not be so dense as to inhibit breathing through the mouth.

Taking off a Mask: Presumably you have finished using your mask in a frequented public place and have returned home. Your mindset should be that there might be viral material on the outside of your mask. First, wash your hands with soap for 20 seconds. Try to remove the mask without touching the outside of it. If the mask comes with rubber bands, use the rubber bands to remove the mask. If you happen to touch the outside of the mask during the removal process, wash your hands before continuing. After the mask is off, wash your hands with soap for 20 seconds. Then wash your face but avoid touching the eyes, nose and mouth.

Reusing a Mask: If you did not go to a frequented place (such as a store or gas station) but to relatively isolated places such as those during a walk and did not encounter anyone who got within 6 feet of you or did not sneeze or cough in your presence, then you can reuse your mask. Your use of a mask in isolated places is to prevent transmission by method (i) if someone should sneeze or cough in your presence. Indeed, if you are confident of not having such encounters, wearing mask is optional. If you went to a frequented place, set your mask aside for 4 days before reusing it. If your mask is made of cloth and you need to reuse it within 3 days, wash it thoroughly with soap and water; Note that frequent washing of a cloth mask may reduce its filtering ability.

Types of Masks

     First of all, any mask offers some benefits for the following reasons: (1) it reduces the chances of infection through transmission by method (i). (2) It helps with preventing people from touching their nose and mouth (transmission by method (ii)). (3) If you should be an asymptomatic covid-19 carrier, you are helping others by not generating viral matter that might infect them. Given these three reasons, it is not surprising that there is evidence that the use of masks is valuable in fighting covid-19 transmission. The evidence of protection of a user via transmission by method (iii), that is, through aerosols, is limited and depends on the quality of the mask and how well it is used; see the discussion below.
     If you happen to have an N95 mask/respirator or medical mask that you have previously used, health care professionals cannot reuse these and it is not unethical for you to use it. If you have any of these masks and they are unused, contact a local hospital for donation procedures. Wearing an N95 provides protection against transmission by method (iii). There is some weak evidence1,2,3 that a well-sealed medical mask is as effective as an N95 for (iii) in real-world settings.
     Readily available handkerchiefs, bandanas and construction worker's dust masks provide the 3 benefits listed in the first paragraph of this section but offer little protection for transmission by method (iii).
     Homemade masks are another option. There are countless YouTube videos on make-it-yourself medical masks. For a disposable mask, one can use several folds (that is multiple layers) of paper towel. In the next paragraph, we argue that if such a mask is airtight and one can just breathe sufficiently through the mouth, then some protection against transmission by method (iii) is obtained. Another option is to use an eye-glass cleaning cloth:

Active Covid-19 Cases in China
An example of a homemade mask.

     Compared to handkerchiefs and bandanas, eye-glass cleaning cloth is denser and provides some protection against transmission through aerosols. You should not use material in a mask that renders breathing through the mouth too difficult.
     There are two tests that one can perform to see whether the penetration of aerosols of the size4 of breath droplets is reduced while wearing a mask. The first is whether it is harder to breathe. Air molecules consist of oxygen, carbon dioxide and nitrogen. These molecules are about 1000 times smaller than breath-generated aerosol droplets. Hence, if the flow of these air molecules is reduced by your mask then the flow the larger aerosol droplets through the mask must be inhibited even more.
     The second test is as follows. First spray some perfume or similar product into the air. Then move into that region, breathe in through the nose and note the amount of smell. Next, put on your mask and repeat the process in another room. If the amount of smell is reduced then your mask is helping to inhibit transmission by method (iii). This is because it turns out the droplets in the aerosols of perfumes are about the same size as those of the droplets in breathe exhalation.5
     Using the perfume test, one can observe that a typical construction worker's dust mask lets most of the aerosol droplets through. One can also observe a significant difference in sealing and not-sealing a mask to render it airtight.
     By the way, theoretically an N95 respirator should be more effective in preventing influenza than a medical mask. However, we mentioned above that three randomized clinical trials involving health care professionals in clinical settings have found little difference. This is good news because it suggests that one does not need the gold-standard N95 to achieve a protective benefit. By the way, the N95 mask was found to be more effective than surgical masks for other types of diseases such as clinical respiratory illness.

On the Effectiveness of Masks for Influenza Protection

     While there is good evidence6 that the use of masks reduced the transmission rate of the SARS virus in 2003, it is unclear as to whether this was due to source reduction (viral matter generation by an infected person) or due to protective effects (prevention of viral matter from entering the nose, eyes or mouth of a healthy person) or both. Since SARS is a coronavirus, masks should be helpful in the battle with covid-19.
     As for the protective benefits of masks for air-borne viruses, there is some evidence of a benefit. In a meta-analysis3 of the effectiveness of masks and respirators against an influenza-like illness for health care workers, a roughly three-fold benefit was noted. The reduction in the risk of getting SARS was seven-fold. Masks and N95 respirators yielded similar benefits.
     In an experiment7 in which surgical masks where exposed to live aerosolized infectious influenza virus, a wide range (depending on the mask type) of reduction of viral exposure behind the mask was observed. The range was no effect to a 55-fold benefit. The average was a six-fold reduction in viral exposure.
     In another experiment,8 subjects wore different types of masks and breathed in floating particles whose size was that of typical viral aerosol droplets. A special device measured the density of particles on both sides of the mask. Tests were done for people performing various activities. The FFP2 mask, which is a European equivalent of the N95, produced reductions in adults ranging from 66-fold to 113-fold depending on the activity. Surgical masks yielded about 4- or 5- fold reductions. A home-made mask made from tea cloth reduced the aerosolt droplets by about 2.5.


1N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial by L. J. Radonovich Jr, M. S. Simberkoff, M. T. Bessesen, et al.
2Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers: A Randomized Trial by M. Loeb, N. Dafoe, J. Mahony, et al.
3Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis by V. Offeddu, C. F. Yung, M. S. Low, and C. C. Tam.
4Cough aerosol in healthy participants: fundamental knowledge to optimize droplet-spread infectious respiratory disease management by G. Zayas, M. C. Chiang, E. Wong, F. MacDonald, C. F. Lange, A. Senthilselvan, and M. King.
5Particle Sizes of Aerosols Produced by Nine Indoor Perfumes and Deodorants by J.-F. Bertholon1, M.-H. Becquemin1, M. Roy, F. Roy, D. Ledur, I. Annesi-Maesano, and B. Dautzenberg.
6Physical interventions to interrupt or reduce the spread of respiratory viruses: systematic review by T. Jefferson, R. Foxlee, C. Del Mar, L.Dooley, E. Ferroni, B. Hewak, A. Prabhala, S. Nair, and A. Rivetti.
7Effectiveness of surgical masks against influenza bioaerosols by B. Makison Booth, M. Clayton, B. Crook, and J. M. Gawn.
8Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population by M. van der Sande, P. Teunis, and R. Sabel.

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