With the amount of COVID-19 infections on the rise, researchers are scrambling to contain its spread. Researchers at the University of Austin-Texas may have found evidence of COVID-19 spreading exponentially through those who are infected but have not yet shown any symptoms.

Using self-reported data on patient’s recollections of when symptoms were first felt – from the initial outbreak region in late January in China – the researchers looked at 468 infection case reports from 93 various cities in China. They calculated COVID-19’s “serial interval” or the amount of time needed for the virus to spread from one person to the next using the data collected.

Serial intervals are calculated by looking at the time it took for one person infected with the virus to infect another individual, or the time interval between infection and subsequent transmission. The serial interval differs from the incubation period because the incubation period is the amount of time it takes for symptoms to show after you have been infected. The serial interval is the amount of time it takes the virus to spread from one person to the next, and so on, like a chain.

“In other words, if person A infects person B, it’s the time from A first feeling sick to B first feeling sick. In contrast, the incubation period is the number of days between a case being infected and the onset of their symptoms,” comments Dr. Lauren Ancel Meyers, the principal investigator of this study. The incubation period for the novel COVID-19, according to the CDC, is anywhere between 2-14 days.

The researchers found that 1 in 10 infections originated from those who later discovered that they had the virus but did not feel sick. COVID-19 was found to have a very short serial interval average at four days, based on the data collected in China. This short serial time suggests that the spread of the virus occurs before symptoms are observed or felt by the infected. This means that the number of outbreaks will grow exponentially and will be difficult to stop unless extreme measures, such as social distancing, isolation, quarantine, school closures, and cancelation of large gatherings, are taken.

Tips on social distancing, illustrated by Gaius.
Tips on social distancing, illustrated by Gaius.

COVID-19’s short serial interval and long incubation period could explain why we see the number of cases spread like wildfire. 

Other infectious diseases with a longer serial interval, such as Ebola, are easier to identify and contain because a longer serial interval – or the time it takes for transmission of infection to take place – makes it easier for healthcare workers to identify and isolate sick people before they can spread the infectious agent (like a virus). Whereas those diseases with a lower serial interval like influenza, and COVID-19, are more likely to spread at a higher rate. 

Although researchers have data that COVID-19 spreads through those who are not showing symptoms, data was collected from the individuals’ recollection of when they were first infected during the early stages of the outbreak in China. This may cause underestimation in serial intervals for COVID-19 (shorter than they actually are) due to recall inaccuracy. 

But other studies have found similar results. A study conducted by Hokkaido University found that the serial intervals they calculated from 28 infectee and infector pairs had a median of around four days. Importantly, these intervals were shorter than COVID-19’s incubation period. The researchers suggest that this means that transmission can occur before the infected person shows symptoms.

As recommended by the Center for Disease Control (CDC), social isolation is the key to keeping the virus at bay. COVID-19, as of right now, is thought to spread through close contact with an infected person and through respiratory droplets when infected individuals cough or sneeze. The spread of the virus can also occur through touching a surface or object that has the virus and then touching your eyes, nose or mouth. Because COVID-19 may spread through individuals who are not showing symptoms,  it is vital to curb the spread and “flatten the curve” through social distancing and quarantine.

Social Distancing

As shown by the study highlighted earlier, the virus spreads through individuals who are feeling well and not showing any symptoms. Governments around the world have ordered students and workers to say at home to prevent the continued spread of COVID-19, and more recently, the number of people allowed in social gatherings in the United States reduced from 50 to 10 people. Concerts and any events that have large crowds of people were all canceled or postponed.

Social distancing is a crucial step in keeping our communities safe. This tactic is used to reduce the spread and transmission of the virus by limiting exposure to the virus within communities. In turn, this protects more vulnerable populations like the elderly, young children, and those who are immunocompromised. By social distancing, and staying at home, the spread of the virus slows, and the risk of being exposed lowers. This also buys more time for hospitals to prepare for an influx of sick patients, and to avoid situations where healthcare professionals are too overwhelmed to treat everyone. 

Social distancing, by Gaius.

Social distancing only works if people stay at home regardless of age or if they are feeling well or not. Avoiding close contact with people is crucial if the virus is spreading within your community. 

The number of confirmed cases is going to go up as testing for COVID-19 becomes available, but it does not mean that social distancing is not working. 

How do we socially distance ourselves?

Socially distancing ourselves means avoiding contact with other people for at least two weeks (this is recommended for virtually the rest of March 2020). COVID-19 has an incubation period of 2-14 days (this is the period between when someone is exposed to the virus and when they feel sick – most people will show symptoms by around 11 days after exposure). Another study conducted by researchers at John Hopkins University found that out of 10,000 individuals exposed, only 100 (so a small proportion) will show symptoms after 14-day monitoring or quarantine period. In other words, most sick people are safe to leave quarantine after 14 days.

We can socially distance ourselves by working from home, avoiding going out in public unless absolutely necessary, and avoiding contact with others. As of right now, in many parts of the U.S, only pharmacies, grocery stores and medical centers are open. Restaurants are offering take-out or delivery only as an effort to keep everyone’s distance. If you must go out, it is recommended you keep a distance of at least 6 feet between others. While cases of COVID-19 may increase when we are social distancing, it is crucial to keep our distance to protect others so the spread may slow down.