Montreal Christian Thinker

SARS-CoV-2 (COVID-19) Transmission – Surfaces vs Droplets vs Aerosols

A lot of people keep thinking that SARS-CoV-2 transmits primarily via fomites (i.e., object surfaces) and mouth droplets. Unfortunately, and actually, SARS-CoV-2 primarily transmits via aerosols, and so a lot of people are not careful enough with masks and physical distancing (e.g., not covering nose, loose masks, not putting mask indoors when it makes sense, but putting mask outdoors when not necessary, etc.). Fomite transmission (i.e., touching surfaces and then transferring to nose, mouth or eyes) is not driving the pandemic as already mentioned by CDC and WHO, or even virologists like Vincent Racaniello, and aerosol specialists like Dr. Jose-Luis Jimenez. Here are CDC’s statements as examples:

https://www.cdc.gov/media/releases/2020/s0522-cdc-updates-covid-transmission.html  (CDC, May 22 2020)

…Based on data from lab studies on COVID-19 and what we know about similar respiratory diseases, it may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes, but this isn’t thought to be the main way the virus spreads….

https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-covid-spreads.html  (CDC, Oct 28 2020)

…Spread from touching surfaces is not thought to be a common way that COVID-19 spreads….

Prof. Emanuel Goldman (Microbiology, Biochemistry and Molecular Genetics, NJ Medical School) published “Exaggerated risk of transmission of COVID-19 by fomites,” in The Lancet (July 3, 2020). He ended his paper with the following:

In my opinion, the chance of transmission through inanimate surfaces is very small, and only in instances where an infected person coughs or sneezes on the surface, and someone else touches that surface soon after the cough or sneeze (within 1–2 h). I do not disagree with erring on the side of caution, but this can go to extremes not justified by the data. Although periodically disinfecting surfaces and use of gloves are reasonable precautions especially in hospitals, I believe that fomites that have not been in contact with an infected carrier for many hours do not pose a measurable risk of transmission in non-hospital settings. A more balanced perspective is needed to curb excesses that become counterproductive.

Other papers have been published with a similar understanding:

Low risk of SARS-CoV-2 transmission by fomites in real-life conditions

Questioning COVID-19 Surface Stability and Fomite Spreading in Three Aeromedical Cases: A Case Series

Rethinking environmental contamination and fomite transmission of SARS-CoV-2 in the healthcare

Understanding air and water borne transmission and survival of coronavirus: Insights and way forward for SARS-CoV-2

SARS-CoV-2 disease severity and transmission efficiency is increased for airborne but not fomite exposure in Syrian hamsters

Community Transmission of SARS-CoV-2 by Surfaces: Risks and Risk Reduction Strategies

Now, I am certain that there would be scientists who would disagree with some of these papers. But I do not see, for example, those disagreements proving the contrary: that fomite transmission is more prevalent than aerosol transmission, or that fomites are more important than aerosols in this context. That is not where the disagreements would lie. This is why I am being cautious with this as I am not a specialist myself.

There are caveats and nuances with all of the above, which led me to posting this blog post.

First, some common people out there who commute in buses and trains, who use subways, who go to store and supermarkets, seem to think that it is only necessary to cover one’s mouth without covering the nose because what might be transmitted are mouth droplets. In fact, I heard many teenagers who commute use this argument, and that is the reason why they only cover their mouth and not their nose. In addition, there are other people who do not cover their nose because they have trouble breathing. This is a legitimate concern and I will not challenge that here since that would be a can of worms. However, it is not the case that SARS-CoV-2 is primarily transmitted by mouth droplets–most cases and super spreader events are not explained by this assumption. Instead, primarily aerosol transmission explains most cases.

Second, all published studies in journal articles must be interpreted in light of a large body of knowledge. If some particular study leans towards the importance of fomites for transmission instead of aerosols, one must ask if they are actually referring or studying this in a clinical, hospital environment (where there is high-risk of transmission) or a non-hospital environment. Evidently, being in a hospital setting is riskier than a work setting where only 10% of employees are physically present and are dispersed in distant cubicles and rarely spend more than a few minutes near each other. These two different settings are incomparable. Also, are they referencing an indoor activity or an outdoor activity? Being indoors with people is riskier than being outdoors, since outdoors the droplets and aerosols become diluted and dispersed into the atmosphere. Also, there is the issue of viral load: there is a need for a viral load (or amount of viral particles–virions–in the surrounding area) to be present for infection to take place. People do not usually become infected because people cross each other in the mall who may be covered or not covered. People become infected in gatherings where they spend more than several to dozens of minutes together…this allows viral loads to increase in the surrounding area, encouraging the intake of virions into people’s upper respiratory tract and mucous membranes. Also, I have learned in the Virology lectures by Dr. Vincent Racaniello that not all virions are infectious. Some virus particles are not infectious due to nucleotide mutations, virion damages (damages to the Spike protein?), or environmental factors that prevent some virions particles from infecting cells. Also, I learned that not all cells are permissive or susceptible to infection: they may not permit virions to get inside or may not be susceptible to getting virions inside. SARS-CoV-2 is not conscious…it will collide randomly with cells and cells that are permissive or susceptible need to have ACE2 receptors to allow the SARS-CoV-2 Spike protein to attach to ACE2 and get inside via endocytosis. From here, people will react in a variety of ways depending on the immune system and dietary factors (e.g., Zinc, Vitamin D, etc.).

In the end, I do not mind if people want to disinfect this or that object, but I better not hear from them bashing comments that attack other people when those other people actually wear masks properly but may not disinfect objects or surfaces. In a similar way, those people who want to disinfect objects or surfaces better be more careful with their masks if they want to be consistent, or if they want to be outspoken about it. The fact is that fomite transmission is not what caused the pandemic nor is it driving it. Fomite transmission is possible, but it is insignificant. Droplet transmission is more important than fomite transmission in non-hospital settings (I don’t know if the same would be true in hospital settings, I think so but I am not sure). Aerosol transmission is real and far more significant than fomites and droplets.