Transmission of SARS-CoV-2 Virus the Cause of COVID-19 Disease - Comparison with Influenza A

Updated: Jan 12

VIctor Luca & Sandy Milne, 6-Apr-20

How does the virus transmit and what can we do about it?



There are four types of influenza virus, A, B, C and D. Human influenza A and B viruses cause seasonal epidemics of disease (commonly known as the flu) almost every winter all over the world.


Influenza A viruses are the only influenza viruses known to cause flu pandemics, i.e., global epidemics of flu disease. We have been fighting influenza for centuries. The battle to protect populations by vaccination is eternal because all viruses change continuously, and as they change, scientists need to modify the vaccine.


Transmission of SARS-CoV-2, the novel virus that causes the COVID-19 disease, came to prominence in Wuhan, China in December of last year. This virus is new, and scientists don't yet know all that much about the virus and the disease, and uncertainty abounds. However, what should be obvious to anyone by now is that this virus is easily transmitted from one person to another. There is general agreement that the main way that the virus spreads is through contact and droplets. Contact means that you touch something that an infected person has touched or contaminated and then by touching your mouth, nose or eyes you become infected yourself. The virus needs to somehow get into the body. Contact transmission is relatively easy to defend against. Simply don’t put your hands anywhere near an entry point to your body and wash, wash, wash your hands. You should wear gloves also but be careful how you take them off as they should be considered contaminated once used. There is a right way and a wrong way. Your hands may have cuts and scratches and these would provide an entry point also, so be careful. Consider your skin a shield.



Droplet transmission is another whole other kettle of fish. A functional definition of a droplet in the present context is a drop of fluid having a diameter in the range 10 - 100 microns. When an infected person coughs, sneezes or even breaths and talks they don’t just produce droplets that fall short distances away from the infected individual. Coughs may produce aerosols. An aerosol is the suspension of a solid or liquid in air. Aerosols such as those listed below, are at the core of environmental problems, such as global warming, photochemical smog, stratospheric ozone depletion and poor air quality.

Examples of aerosols include dust, fume, smoke, fog and mist. Bio-aerosols may include bacteria, fungi, viruses and pollen. For reference, pollen grains can range from 20 - 100 microns and cause many of us plenty of respiratory grief.

See figure below for an electron microscope image of a selection of pollen grains. Note that the spikes look similar to the SARS-CoV-2 virus particle.

Countdown shopper properly equipped and having a cigarette while he waits to enter the store. The smoke is an example of an aerosol.



So an aerosol is a suspension of fine particles or fluid droplets that are a lot less than 10 microns in diameter. Think of fly spray or what your breath looks like on a cold winter’s day or the smoke a smoker generates. Aerosols, depending on their size, can remain suspended for more than 30 minutes and travel large distances. In fact when we cough, sneeze, breath and talk we produce a range of droplet sizes, some relatively large that fall short distances and some very fine that remain suspended in the air.

The scientific community has been arguing for years whether influenza A can be transmitted as an aerosol. The term ‘airborne’ is also used for aerosol.

Electron microscope image (500x magnification) of pollen grains from a variety of common plants.


Our reading of the past and current scientific literature is leading us to the conclusion that there is very good evidence to suggest that influenza A transmission via aerosols could potentially be an important transmission mechanism. It would certainly explain the infectiousness of the disease and why we have never been able to rid ourselves of it after 100 years or more of battle. If airborne transmission is viable for influenza A, then why would it not also be viable for SARS-CoV-2, the cause of COVID-19 disease. The two viruses are in many ways similar viruses. Nevertheless, the US Centers for Disease Control and Prevention and the World Health Organization have not ruled this mode transmission in. But nor have they ruled it out. And we in New Zealand appear to be waiting from a message from on high before taking action.


Both the influenza A virus and SARS-CoV-2 are corona viruses. The word corona means ‘crown’ in Latin and refers to the spike proteins that surround the outer membrane shell. Both viruses carry Ribonucleic Acid (the molecule responsible for replication) and they cannot replicate without a host cell; viruses are parasites. The influenza A virus has a diameter of around 100 nanometers (0.1 microns). And guess what; so does the SARS-CoV-2 virus? See the electron microscope images of these two viruses below. Note that the colors are fake. An electron microscope is a powerful microscope that can achieve magnifications much larger than the optical microscopes most people will be familiar with.


You don’t have to know much about viruses to see the similarity in size and general appearance of these two viruses.


Since these virus particles are essentially made up of the same elements including carbon, hydrogen, nitrogen, phosphorus, oxygen, they have approximately the same density, and since the size and density is similar they should easily be able to become airborne. If influenza A virus can become airborne as the science suggests, then so can SARS-CoV-2.



Since COVID-19 is a potentially deadly respiratory infection, if the tiny virus particles remain suspended in the air we are breathing, then they can end-up going directly into our lungs, and that is a huge problem.


Confined spaces are not good places to be when there are airborne deadly virus particles present. The best practical protection that is available at the moment is an appropriate face mask. By appropriate, we mean a mask that can filter out virus particles with high efficiency. You may have heard a lot about a mask designated as N95 and/or P2. The masks are made of a material that acts like a sieve. The holes or pores in the mask material have to be about the same size as the virus particles.


The masks are made of a material that acts like a sieve. The holes or pores in the mask material has to be about the same size as the virus particles. An N95 masks filters out particles larger than 0.6 micron with 95% efficiency, hence the 95. For various reasons that I shall not go into, even though the pores in the mask material are slightly larger than the virus particle, the mask is sill effective.


The idea of a mask is not just to protect you, the wearer, from infection, it is also about protecting others in case you yourself are infected. Be considerate!!

Any protective gear that is used to protect against SARS-CoV-2 infection is only useful if you use it properly. You must remember that any barrier that you put between yourself and the virus, itself becomes contaminated if you are in an environment where virus is present in high concentration.


In the meantime the age old refrain “discretion is the better part of valor” has never been more applicable and it will cost you nothing.

To any reader that doesn’t understand what we have tried to explain here, please feel free to contact us, and further explanation will be provided.


Note added in proof: Since publishing the above article in The Beacon of 6-Apr-20 much more information has come to light on the virtues of using face masks to protect against COVID-19. The evidence of airborne transmission has also solidified. I will deal further with this matter in another post.

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