Asymptomatic transmission, age, and COVID19
Why it “takes a village” (including you) to end a pandemic
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It is important to note this post was written on March 27, 2020. The COVID19 pandemic is a rapidly developing situation, and thus, some information may change at a later date. This article reflects the reported data available as of March 27, 2020.
Our lives have been dominated by COVID19; we see it daily on the television, highlighted in the news, and trending on our social media. The entire situation feels overwhelming and there are valid reasons to be concerned (check out Why are we so worried about a virus that’s ‘only’ killed 21,000 people worldwide?). It is important to remember that each and every one of us has an imperative role to play in reducing the transmission of the virus. Our collective cooperation and adherence to public health strategies can and will save lives.
Pre-Symptomatic cases of COVID19: How virus shedding can fuel a pandemic
The symptoms of COVID19 include fever, cough, and shortness of breath. A person infected with SARS-CoV-2, (the virus that causes COVID19), could experience any combination of these symptoms... or surprisingly, none at all. People who have a disease but show no symptoms are described as being asymptomatic. Individuals who are actively infected with SARS-CoV-2 can be classified into one of three groups based upon how they develop symptoms:
Symptomatic: Individuals with COVID19 who are actively experiencing fever, cough, and/or shortness of breath, among other potential symptoms. Mild cases can be treated at home, while severe cases require hospitalization.
Presymptomatic: Individuals with COVID19 who are not yet actively experiencing symptoms (temporarily asymptomatic), but will go on to exhibit symptoms at a later time. These individuals are likely unaware that they are infected.
Asymptomatic ‘carriers’: Individuals with COVID19 who are not and will not experience symptoms. These individuals are likely unaware that they are infected. Early studies have shown that about 1-3% of people who are infected will never experience any symptoms.
This distinction in symptoms leads to a key question for this pandemic: Can people with presymptomatic infection of SARS-CoV-2 still transmit the virus? There is increasing evidence that yes, presymptomatic transmission of the virus has occurred. This means that even in people who feel completely healthy, if they are infected with SARS-CoV-2, the virus may still be able to replicate and “shed.” In virology, we use the term “shedding” to describe how viruses can exit a person’s cells and ultimately, their body. When an infected person sheds virus, they disseminate it into their surroundings. This can happen when someone coughs, sneezes, or touches their nose or mouth. Newly shed viruses can reside in the air within microscopic droplets, or come to rest on a surface. If uninfected individuals come into contact with these viruses, they risk being infected.
Visualization of how social distancing can limit transmission of a viral disease like COVID19. The red ‘bubbles’ represent viral shedding. Animation courtesy of Griffin Haas.
Presymptomatic transmission is why social distancing is key to ending this pandemic. A person who feels completely healthy could be shedding the virus, transmitting it to their friends, coworkers, or fellow commuters. It’s worrisome that the incubation period of COVID19—the time in which a person is presymptomatic—is 2-14 days, because we don’t know exactly when a presymptomatic person could be shedding virus. It’s easy to imagine the unfortunate consequences of a presymptomatic individual who commutes on the subway, unaware they are putting others at risk for as long as 2 weeks. Long-term social distancing can effectively prevent such ‘chains of transmission’ from occurring, ultimately protecting vulnerable populations. What makes social distancing effective is that it physically separates the individuals shedding virus (both presymptomatically and symptomatically) from uninfected individuals. Without physical contact with the virus, an uninfected person cannot become sick. The longer this physical separation is maintained, the longer residual infected individuals have to recover and stop shedding virus.
Visual representation of how viral shedding facilitates transmission in public spaces; such transmission events can be decreased with stringent social distancing. GIF courtesy of Griffin Haas.
Age and COVID19 - Who are the vulnerable populations?
The severity of COVID19 symptoms varies between cases, but more severe cases have been associated with older age and underlying medical conditions. This means that the prognosis of a COVID19 patient—the predicted course of the disease a patient experiences—worsens as the patient’s age increases. Likewise, underlying medical conditions such as hypertension, cardiovascular disease, diabetes, chronic respiratory diseases, and cancer as well as a history of smoking also appear to be risk factors for a poor prognosis.
Data and figure courtesy of The Centers For Disease Control and Prevention, MMWR Morb Mortal Wkly Rep 2020;69:343-346, published March 18, 2020.
The Centers for Disease Control and Prevention reports that between February 12 and March 16, 31% of COVID19 cases, 45% of related hospitalizations, 53% of related ICU admissions, and 80% of COVID19-related deaths in the United States occurred among adults aged at or above 65 years. Essentially, COVID19 patients older than 65 often experience severe symptoms. However, being a young (20-40) adult does not guarantee a mild case of COVID19, and thus everyone —young adults included—should make efforts to wash their hands often and practice social distancing, both for themselves and for the health of others.
Fortunately, children and adolescents appear to have mostly mild symptoms, with very few reported hospitalizations or deaths in kids under the age of 18. However, even if kids only experience mild symptoms, they are still thought to be capable of transmitting the virus to others. Children are likely asymptomatic carriers of SARS-CoV-2. This is one reason schools across the country have closed—not so much to protect students from serious COVID19 effects, but to keep children from spreading the virus to their teachers and caretakers. Additionally, parents and guardians should ensure their children practice social distancing measures too. This means no playdates, no visiting high-traffic areas like playgrounds, and no attending group events such as birthday parties. Taking measures to prevent potentially sick children from interacting with susceptible individuals (such as grandparents, immunocompromised individuals, or those with underlying medical conditions) is critical for preventing transmission to vulnerable populations.
Image courtesy of The Centers for Disease Control and Prevention.
It takes a village: What you can do to limit COVID19
Regardless of risk status, all of us are capable of contracting and transmitting SARS-CoV-2 as long as community transmission is sustained.
So what can you do?
Continue to practice social distancing: Work from home if possible, avoid large crowds, and limit the number of people you are in close contact with. The longer we practice social distancing, the less cases of COVID19 we will have.
Wash your hands often, using soap and warm water: Do this even while you are at home, and especially when returning from public spaces. Soap and warm water can ‘kill’ SARS-CoV-2, rendering the virus unable to infect you.
Protect vulnerable populations: Offer to purchase groceries for older individuals to reduce their risk of exposure to the virus in public settings. Limit physical visitation with vulnerable people, and try to adopt virtual forms of communication if possible.
If you are sick, isolate yourself from others and practice good hygiene: Stay at home, wash your hands often, and cough/sneeze into your elbow or into a tissue. Take measures to avoid exposing others to the virus. Know when to seek medical attention if symptoms become severe.
Courtesy of Toby Morris (@XTOTL on Twitter) via TheSpinoff.co.nz. This animation shows how our collective efforts to practice social distancing can reduce transmission of SARS-CoV-2.
Public health measures such as practicing good hygiene and engaging in social distancing are key to ending this pandemic. They rely on the population—each and every one of us—to be effective. We’ve all heard the adage “it takes a village to raise a child”; this saying is often used to describe the collective social responsibility of a community to create a fostering environment. Likewise, it “takes a village” for public health measures to be effective. We are all ascribed to the social responsibility of maintaining public health. The collective decision by our communities to social distance—to work from home, to avoid large gatherings, and to limit the number of interactions we have with others—can and will prevent cases of COVID19. Do your part to flatten the curve.
Griffin Haas
Griffin is a PhD Student at the Icahn School of Medicine at Mount Sinai who received his B.S. in biology from Duke University.
Griffin joined the Benhur Lee lab in 2020 and has since been involved in projects related to henipavirus/host protein-protein interactions. He is highly interested in emerging pathogens and how such viruses interact with their hosts during infection. Griffin is also interested in exploring ways to creatively visualize biological processes and enjoys generating graphics related to microbiology and infectious diseases.
Email: griffin.haas@icahn.mssm.edu
Twitter: @GriffinHaas