How does COVID-19 spread?

In this series of posts, we will talk about the biological side of COVID-19, as understood by a high school student. Click here to view previous articles.

4 min readJun 13, 2020

Recently, Dr. Maria Van Kerkhove, head of the World Health Organization’s emerging diseases and zoonosis unit, issued a statement that stirred up some controversy. When addressing contact tracing data, Dr. Kerkhove stated the following:

“We have a number of reports from countries who are doing very detailed contact tracing. They’re following asymptomatic cases, they’re following contacts and they’re not finding secondary transmission onward. It is very rare — and much of that is not published in the literature… We are constantly looking at this data and we’re trying to get more information from countries to truly answer this question. It still appears to be rare that an asymptomatic individual actually transmits onward.”

The WHO downplaying the risk of asymptomatic transmission was met with great backlash from organizations such as the American Centers for Disease Control and Prevention (CDC) and many other scientists. This isn’t the first time the WHO has come under scrutiny for some of its claims, which is concerning considering that the agency influences lockdown policies in nations across the globe. In fact, the whole concept of extensive social distancing is based upon the principle that asymptomatic carriers play a significant role in spreading the disease. In this article, we will be taking a look at what the current consensus is in the virology community regarding the mechanism whereby the SARS-CoV-2 virus spreads.

Respiratory Droplet Transmission

The first, and most prominent, way that COVID-19 spreads is through respiratory droplets, which are defined as droplets larger than 5–10μm (micrometers) in diameter. These droplets are released into the air when an individual coughs or sneezes. There is no conclusive evidence thus far, but talking might also play a significant role in releasing respiratory droplets. These droplets are transmitted when they land in the mouth, nose, and even eyes. Therefore, it is possible to get infected when through direct and indirect contact. Direct contact would occur in instances where respiratory droplets are released due to a sneeze or cough towards another individual in close proximity. Experts approximate this “close proximity” to be around 6 feet. Indirect contact would occur in instances when an individual is in contact with an object or surface previously contaminated by an infected individual and proceeds to touch their face with their hands. The virus can last on certain surfaces (depending on material) for as long as a couple of days, so it is important to properly disinfect all frequently used objects and surfaces.

Airborne Transmission

It is still debated whether airborne transmission plays a role (or is even possible in the first place) in spreading COVID-19. However, many experts believe that it is possible under certain circumstances and that people should take appropriate precautions accordingly. Although respiratory droplet transmission does occur through the air to a certain extent, it does not fall under the category of airborne transmission. Airborne transmission occurs when disease-causing microbes present in droplet nuclei, which are droplet particles smaller than 5μm in diameter, are inhaled into the lungs. Due to their small size, droplet nuclei linger in the air for long periods of time and move with air currents, which can carry them great distances. Although research around airborne transmission is constantly evolving, scientists currently estimate that COVID-19 causing droplet nuclei can remain in the air for as long as 3 hours. The capability of airborne transmission makes diseases far more contagious, however, it doesn’t appear to be the primary form of transmission in COVID-19.

What does this mean?

With no vaccine close in sight, the only way to prevent further spread of COVID-19 is to prevent exposure and transmission from occurring in the first place. The uncertainty over asymptomatic doesn’t provide any information either. Thus, it is important that individuals, whether symptomatic or asymptomatic, regularly practice recommended precautionary measures such as handwashing, social distancing, and mask-wearing in public. This will especially be challenging in schools, work-places, and other places that are currently shut down. In the next article, we will take a look at the chemistry of soap and why it is so effective in killing viruses.

References

Coronavirus (COVID-19) frequently asked questions. (2020, June 02). Retrieved from https://www.cdc.gov/coronavirus/2019-ncov/faq.html

How to Protect Yourself & Others. (2020, April 24). Retrieved from https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html

Is coronavirus airborne? COVID-19 transmission. (n.d.). Retrieved from https://www.medicalnewstoday.com/articles/is-coronavirus-airborne#is-it-airborne

Jorge, K. (2020, June 09). WHO clarifies asymptomatic COVID-19 transmission, says much is unknown. Retrieved from https://fox17.com/news/local/asymptomatic-spread-of-coronavirus-appears-to-be-very-rare-who-says

Mandavilli, A. (2020, June 09). In the W.H.O.’s Coronavirus Stumbles, Some Scientists See a Pattern. Retrieved from https://www.nytimes.com/2020/06/09/health/coronavirus-asymptomatic-world-health-organization.html?auth=login-google

Modes of transmission of virus causing COVID-19: Implications for IPC precaution recommendations. (n.d.). Retrieved from https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations

Nazario, B. (2020, June 09). How Coronavirus Is Transmitted: Here Are All the Ways It Can Spread. Retrieved from https://www.webmd.com/lung/coronavirus-transmission-overview#1

Offord, C. (n.d.). How COVID-19 Is Spread. Retrieved from https://www.the-scientist.com/news-opinion/how-covid-19-is-spread-67143

UC San Diego News Center. (2020, April 09). Retrieved from https://ucsdnews.ucsd.edu/feature/a-deep-look-into-the-biology-and-evolution-of-covid-19