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  • Omie Mills, M.D.

COVID-19 (Part 1): Knowledge to prevent or minimize infection


2020 has been an unusually difficult year for most. COVID-19, in particular, has contributed to the physical, mental, spiritual, social, and political tensions in many lives. Members of my immediate family have been directly affected with the illness. In response, I began to research the scientific literature on this topic, as I believe that part of the stress of COVID-19 comes from a lack of understanding of the coronavirus that causes COVID-19 and from a lack of awareness of how to prevent or minimize infection.

In this blog, we will learn more about COVID-19 and how it compares to other illnesses such as the flu, what symptoms might indicate COVID-19, what type of testing is available, how to avoid an infection, the various courses an infected individual may take, and how the immune system responds.

What is COVID-19?

COVID-19 is a respiratory illness caused by the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) which is a type of coronavirus that infects people in many different ways.

Coronaviruses are a large family of viruses that have been around for a long time. Seven known types of these viruses can infect people. The coronavirus that causes COVID-19 has probably been around for some time as well, but is thought to have recently crossed over from animals into people and was discovered by scientists in 2019 (1).

Some believe that SARS-CoV-2, the virus that causes COVID-19, was being developed as a biological weapon in a lab in Wuhan, China, and that a laboratory worker was infected, from which it spread to others, though a defense expert, Dr. Mark Kortepeter, a physician and biodefense expert who formerly worked at the U.S. army “hot zone” research lab, suggests SARS-CoV-2 lacks sufficient properties to make it a good choice for military purposes (see the link below for more information).

What symptoms might I have if I am infected with SARS-CoV-2?

The Centers for Disease Control (CDC) reports that “Infected people have had a wide range of symptoms reported – from mild symptoms to severe illness. Symptoms may appear 2-14 days after exposure to the virus" (2).

People with these symptoms may have COVID-19: (2)

Fever or chills


Shortness of breath or difficulty breathing


Muscle or body aches


New loss of taste or smell

Sore throat

Congestion or runny nose


Nausea or vomiting

If someone is showing any of the following emergency warning signs, seek emergency medical care immediately:

Trouble breathing

Persistent pain or pressure in the chest

New confusion

Inability to wake or stay awake

Bluish lips or face

How do people get infected with SARS-CoV-2 that causes COVID-19?

The coronavirus that causes COVID-19 can be inhaled on droplets or as virus particles that have come from an infected person that releases the virus into the air when breathing, speaking, coughing, sneezing, or singing. This occurs more when that person is not wearing a face mask (3, 4, 5, 6, 7, 8).

In other cases, you may touch something that has coronavirus on it, and then infect yourself with the virus by touching your face. If you are living with someone who has COVID-19, your risk of becoming infected is much higher (9).

What can I do to prevent myself and others from being infected with the SARS-CoV-2 that causes COVID-19?

University of California San Francisco infectious disease specialist Peter Chin-Hong, MD likes the “Three W’s to ward off COVID-19:” wearing a mask, washing your hands, and watching your distance.10 “There’s little evidence that fomites (contaminated surfaces) are a major source of transmission, whereas there is a lot of evidence of transmission through inhaled droplets, said Chin-Hong” (10).

While washing your hands and watching your distance are generally less debated, the wearing of masks to prevent infection has become a political issue rather than a scientific one, “pitting those willing to follow health officials’ guidance and cover their faces against those who feel it violates their freedom or buys into a threat they think is overblown” (11). An initial shifting of federal recommendations have muddied the water.

Scientific studies support that “Masks are primarily intended to reduce the emission of virus-laden droplets (“source control”), which is especially relevant for asymptomatic or presymptomatic infected wearers who feel well and may be unaware of their infectiousness to others, and who are estimated to account for more than 50% of transmissions” (12, 13). So masks help to prevent virus-laden respiratory droplets from an infected asymptomatic or symptomatic wearer from reaching others. Masks also help reduce inhalation of these droplets by the wearer (“filtration for personal protection”) (14).

“My mask protects you, your mask protects me.” Unknown

Masks reduce transmission of the virus through both mechanical filtration and electrostatic filtration (15). Human studies of masking and transmission of SARS-CoV-2 show reduced transmission of 70-79% within households containing both infected and non-infected persons, and during high-risk exposures (16, 17, 18, 19, 20). “Universal masking” studies in communities showed a significant decrease in new infections, and reductions in mortality (21, 22, 23, 24, 25, 26, 27). Masking may also reduce the dose of virus the wearer might receive, resulting in a mild or even asymptomatic infection. Larger viral doses result in a more aggressive inflammatory response (28). It is important to note that openings and gaps found around the edge of the mask and facial contours can degrade the performance of the mask (29).

What type of mask should I wear to prevent infection with SARS-CoV-2?

Peter Chin-Hong, MD notes the bottom line is any mask that covers the nose and mouth will be of some benefit. “The concept is risk reduction rather than absolute prevention,” said Chin-Hong.

“You don’t throw up your hands if you think a mask is not 100 percent effective. That’s silly. Nobody’s taking a cholesterol medicine because they’re going to prevent a heart attack 100 percent of the time, but you’re reducing your risk substantially” (10).Peter Chin-Hong, M.D.University of California San Francisco Infectious Disease Specialist

A study of cloth masks suggests that cloths with high threads-per-inch such as cotton, natural silk, and chiffon provided the best protection from aerosol particles (15).

Can wearing a mask hurt me? Am I in danger of breathing in too much carbon dioxide from wearing a mask?

Fresh air is a well known booster of immunity and health, and should be sought after at every available opportunity. But in cases of close contact with potentially infected air, the slightly less than fresh air found inside of a mask will usually be less hazardous to the wearer than catching COVID-19.

Of note, however, some adverse effects have been reported by healthcare workers who have had to wear N95 masks for prolonged periods of time (i.e. headaches, acne, rash, impaired cognition) (30), and some studies have shown that some people may experience a decrease in oxygen or increase in carbon dioxide when wearing an N95 mask (31, 32). But will the effects be the same in a cloth mask?

The size of pores in varying types of masks should be better understood in order to draw more accurate conclusions. For consideration, it is important to know that the coronavirus is 0.12 microns in diameter. The N95 mask protects down to 0.1 microns with 95% efficiency and is where it gets its name (33). A surgical mask has a 0.3 – 10 micron pore sizes, which is much larger than the coronavirus (34). Cloth masks vary in pore shape and mean pore size, and in one study, the sizes of pores in cloth masks ranged from 81 to 461 microns (35).

Though it sounds as though the pore size in both surgical and cloth masks would not be able to protect you from the virus, in everyday settings, it is important to know that the virus doesn’t travel alone. COVID-19 viruses are usually carried around by respiratory droplets (36). Studies have shown that non-N95 masks including cloth masks can block these droplets effectively (but not entirely) (4, 5, 6, 7, 8). Distance from the infected person must also be considered as the concentration of aerosols is in highest concentration close to infected persons and dissipates with distance (37). Thus the importance of following the additional recommendation to remain six feet or more apart from others is better understood.

While considering the size of particles that may pass in and out of cloth masks, for the healthy mask wearer, dangerously low levels of oxygen or high levels of carbon dioxide are unlikely. If we consider size again, the coronavirus that causes COVID-19 is about 0.12 microns in diameter (33). A molecule of carbon dioxide is approximately 0.00033 microns wide and oxygen is almost the same (36). This is approximately 1000 times smaller than the coronavirus. “To help us picture the difference, let’s estimate that the period you see at the end of this sentence is about 1 millimeter wide. If we pretend the period represents a molecule of oxygen or carbon dioxide, then the virus would be about the size of a meterstick!” One meter stick is approximately 39 3/8 inches long or over 3 feet. The N95 mask, using the same scale would have just small enough pores to block 95% of the meter sticks, but could not stop the period-sized oxygen and carbon dioxide from passing in and out. But because coronavirus travels on respiratory droplets, much larger than the virus alone (36), cloth masks help prevent the spread of COVID-19. Non-N95 masks have been shown to prevent infection in 70-79% of wearers or to decrease the viral load taken in by the mask wearer (16, 17, 18, 19, 20).

How is COVID-19 similar to or different than the usual flu (influenza)?

Similarities (38):

  • Similar presentation – Both influenza and COVID-19 cause respiratory disease with illnesses ranging from asymptomatic or mild to severe disease and death.

  • Transmission – Both viruses are transmitted by contact, droplets, and fomites (objects on which the virus is located such as countertop, door knob, etc.)

  • Hand hygiene and good respiratory etiquette (coughing into an elbow or preferably a tissue) can help prevent both infections.

Differences (38):

  • Loss of smell (anosmia) or taste (ageusia) – COVID-19 sometimes causes these symptoms. The flu does not usually affect a person’s sense of smell or taste (39).

  • Time from infection to symptoms – Influenza has a shorter time from infection to the appearance of symptoms (1-4 days) (40), compared to COVID-19 (2-14 days) (41).

  • Speed of transmission – Influenza can spread to other people faster (3 day serial interval) than COVID-19 (5-6 day serial interval). Serials interval refers to the time between successive cases in a chain of transmission (42).

  • Children – are more likely to pass on influenza than COVID-19.

  • Disease severity – In COVID-19, 80% are mild or asymptomatic, 15% have severe infection, 5% have a critical infection requiring intubation. Influenza does not show as many severe or critical infections as COVID-19.

  • At risk – Those most at risk for a severe influenza infection include children, the elderly, pregnant women, the immunosuppressed, and those with underlying chronic diseases. Those at risk for COVID-19 include those of older age and those with underlying chronic diseases.

  • Mortality – COVID-19 appears to have higher mortality rates than for influenza. The data continues to change as the confirmed numbers of cases and deaths due to COVID-19 are reported, and can be followed at the following link:

At the time this paper is being written, the case mortality rate for COVID-19 in the United States is 1.8%. Mortality for seasonal influenza is below 0.1% (38). From these numbers, we can ascertain that COVID-19 is approximately 18 times more deadly than the flu, though this especially applies to those with higher risk factors such as underlying chronic disease and advanced age.

When should I check to see if I am infected with SARS-CoV-2 that causes COVID-19?