Why Does Disease Spread so Fast?

Authors: Chad Cai, Jiayi Chen, Hill Huang, Charles Zhao, Lambert Zheng, Leon Zhou

Editors: Tiffany Chan, Joyce Hai, Demi Leng, Ethan Liu, Katelyn Ma, Lydia Ren, Shannon Tan, Tyler Vazquez, Molly Zhao

Artists: Tiffany Chen, Jane Liu, Nicole Wang, Nicole Wei

Different Transmission Types

To understand the fast spread of the current novel coronavirus, it is important to first introduce different transmission methods of other diseases. Common transmitting agents include sneezing, coughing, bodily contact, sharing needles, and fecal-to-oral contact. For instance, HIV requires direct sexual contact or shared bodily fluids (blood, seminal and vaginal) for others to be infected. This type of transmission makes HIV relatively difficult to spread in regular day-to-day contact. On the other hand, for COVID-19, respiratory droplets can be transmitted up to a distance of six feet from sneezing or coughing.

Although people tend to believe that the coronavirus cannot thrive without a host, a study from the New England Journal of Medicine found that viruses can still be infectious in the air or on surfaces for various periods, ranging from hours to days. When fluids, such as mucus and respiratory droplets, are left on a surface (doorknobs, pens, or credit cards), the virus can still cause infection. Another way that viruses spread is when people come in close contact with infected individuals. Schools, parties, and other gatherings have a high density of people, thereby increasing the risks of infection. The reason the virus spreads among people so rapidly is because of the asymptomatic "super shedders"; they are individuals who carry the disease but do not show regular symptoms (difficulty in breathing, fever, new loss of smell or taste, and vomiting) of COVID-19. Many of them have not been tested and carry the virus around with them without realizing they have it.

According to Dr. Jeffery Shaman from Columbia University, “these undocumented infections were about half as infectious per person as a documented case who has more severe symptoms and maybe shedding more. Undocumented infections drive the spread and growth of the outbreak”. Thus, one can catch COVID-19 from someone who has not been tested; someone who may be in perfect health can transmit SAR CoV-2 to others who are more vulnerable. These statistics and laboratory results serve critical roles in examining the rapid global spread of COVID-19.

Comparison of Transmission Methods of COVID-19 to Previous Infectious Diseases

The novel coronavirus, commonly known as SARS-CoV-2, carries its namesake due to its genetic relation to the virus that triggers Severe Acute Respiratory Syndrome, SARS-CoV-1. The transmission methods of SARS-CoV-1 are similar to those of the novel coronavirus. Both have spread among birds and mammals via respiratory droplets. Patients of SARS-CoV-1 can also infect others with the virus through close contact. If patients cough or sneeze without coverage, infection is likely to occur. However, according to Dr. Sandra Gonzalez Gompf, for SARS-CoV-1 to spread, people must be relatively close, around 3 feet, which is closer than the ubiquitous 6 feet of safe ¨social distancing¨ that has been announced to the world's populace. Moreover, SARS-CoV-1 can survive on metal, glass, and plastic for up to three days, according to a recent study published in the New England Journal of Medicine. This is remarkably similar to SARS-CoV-2. If one comes into contact with an object containing SARS-CoV-2 and touches their facial orifices, infection may occur. This is quite common among coronaviruses, especially SARS-CoV-2.

H1N1, otherwise known as the swine flu, is another infectious disease that can be compared to COVID-19. H1N1 can be transmitted if one comes into direct contact with swine; through zoonosis (transmitted to humans from animals), H1N1 may also spread to and among humans. However, H1N1 generally appears as a seasonal flu virus, which is less destructive than COVID-19; despite this, transmission methods are similar to the novel coronavirus. Both spread among people through respiratory droplets. One can also become infected if they touch objects that carry the H1N1 virus and then touch their mouth, nose, or eyes.

Transmission methods of these infectious diseases are quite similar, albeit making them difficult to detect early. Not only are they spread by respiratory secretions, but the incubation period of these diseases are relatively long as well. This makes distinguishing healthy people and asymptomatic people difficult without incessant testing.


Do not be misinformed. The coronavirus is a virus family, named after its crown-shaped protein shell. Seven coronaviruses exist in nature, yet among them, only three can cause severe dangers. While COVID-19 has been the most recent hot topic, another coronavirus that is relatively less mentioned in the Middle East Respiratory Syndrome (MERS).

Discovered in Saudi Arabia in 2012, the first major outbreak of MERS occurred in Western Asia. Studies have discovered that MERS was transmitted to humans from dromedary camels, camels with a singular hump. Similarly, all available evidence for COVID-19 indicates a zoonotic source, and its genetic resemblance to SARS suggests that its ecological origin is within the bat population.

MERS possesses a much weaker ability in regards to transmission rates. Only those who come into contact with a patient, such as a doctor without protective measures, possess the risk of infection. Thus, many cases of MERS were often clustered in medical care units. Meanwhile, COVID-19 travels from host to host extremely easily and in a variety of ways, such as through saliva.

The hauntingly plentiful methods in which COVID-19 spreads may account for the multitude of cases that have been identified worldwide. The number of cases soared in February and March, during which the pandemic began rapidly spreading in Europe and America. Yet, so far, 8 years after the first case, only 2,494 MERS cases have been confirmed by the WHO. On the other hand, the death rate among all COVID-19 cases is only around 5%, while the figure for MERS is over 30%.

There has been no effective cure developed for MERS thus far. The only thing doctors can do is to “support” the patients and hop