The COVID-19 pandemic has had several unexpected side effects, including an expansion of our collective vocabulary. Two newly common (and commonly confused) terms in the new global glossary, “asymptomatic” and “presymptomatic,” play a significant role in discussions about the current pandemic.
The distinction is subtle but important, both in communicating with healthcare professionals and in understanding how COVID-19 spreads.
• Presymptomatic describes an ailment that has not yet caused symptoms but will.
• Asymptomatic describes a disease, illness, or infection that causes no symptoms.
Though these terms have been popularized by the COVID-19 pandemic, they also apply to contexts outside of COVID-19.
Cancer, diabetes, HIV, the flu, and colds are among the most common ailments that can sometimes be asymptomatic (for part or all of their course), though many other illnesses produce asymptomatic cases and have asymptomatic phases. COVID-19 also appears without symptoms in many people, one of its many peculiar and troubling qualities.
People infected with COVID-19 do not necessarily show symptoms.
Exactly what percentage of COVID-19 cases are asymptomatic has been researched and estimated many times over the course of the pandemic, but the World Health Organization (WHO) estimates that one in three COVID-19 cases will be asymptomatic, a statistic corroborated by a 2021 study that concluded that asymptomatic infections account for 35 percent of all COVID-19 cases. (Other studies have come up with different results.)
People who have asymptomatic COVID-19 and are therefore unaware of being infected may not seek medical diagnosis, which has significantly complicated controlling the virus’s spread.
People with asymptomatic and presymptomatic COVID-19 can and do transmit the disease. A study early in the pandemic concluded that approximately half of all COVID-19 infections were caused by transmission from people with asymptomatic or presymptomatic COVID-19. Research by University of Chicago Medicine reported a similar figure regarding asymptomatic and presymptomatic transmission: about 50 percent.
People who are unaware that they are carrying and potentially spreading the COVID-19 virus have been dubbed “silent carriers.” Those with asymptomatic and mildly symptomatic cases of COVID-19 have been found to exhibit comparable viral loads, meaning the amount of active virus in and potentially escaping from their bodies is similar. This, in combination with the fact that people with no symptoms are far less likely to take preventive measures such as social distancing, could explain why “silent transmission” rates are so high.
The prevalence of asymptomatic COVID-19 cases makes testing extremely important for people who have had a known exposure to COVID-19. If you suspect you have been exposed to COVID-19, find a testing facility near you.
COVID-19 symptoms typically show up about two to five days after the time of exposure, but they can take as long as 14 days to appear. The time between infection and symptom display is called the incubation period. An infection cannot truly be ruled asymptomatic until the maximum allowance for incubation has passed. Infected people are usually contagious before symptom onset.
The incubation period for the Omicron variant is lower, with an average closer to three days.
People with asymptomatic COVID-19 may experience a variety of symptoms weeks or months after the initial infection. This phenomenon affects both symptomatic and asymptomatic people and goes by several names: long COVID, long-haul COVID, chronic COVID, post-acute COVID-19, and post-COVID conditions.
The CDC (U.S. Centers for Disease Control and Prevention) defines long COVID as “a wide range of new, returning, or ongoing health problems people can experience four or more weeks after first being infected with the virus that causes COVID-19.” Common symptoms include:
• Fatigue
• Brain fog
• Shortness of breath
• Heart palpitations
• Chest and stomach pain
A large data study by the independent non-profit FAIR Health suggests that about 19 percent of people with asymptomatic COVID-19 develop symptoms of long COVID. Though more time and research are necessary to fully grasp the long-term effects of COVID-19, the study references theories as to what causes long COVID, including “persistent immune activation after the acute phase.”
COVID-19 can cause an immune response without causing symptoms. The CDC explains that this response could cause the immune system to mistakenly target healthy cells, causing tissue damage and inflammation that go undetected until long after the active illness has resolved. A 2020 study found lung abnormalities in many people who had recovered from COVID-19, including asymptomatic cases, providing further proof of COVID-19’s longer-term effects, even when no initial symptoms are felt.
In addition to brain fog, new or increased anxiety and depression have been reported by many people recovering from asymptomatic and symptomatic COVID-19. Ongoing research aims to determine which symptoms are caused by the virus’s neurological effects, and which are stress responses to the ongoing burden of the pandemic.
Being vaccinated does increase the likelihood that a breakthrough infection will be asymptomatic, if one occurs at all.
A UK study published in mid-2021 indicates that along with a lower viral load, vaccinated people with a breakthrough COVID-19 infection were less likely to develop symptoms than their unvaccinated counterparts.
CDC literature details the effectiveness of the COVID-19 vaccine in preventing and diminishing the effects of COVID-19 on individuals. Getting vaccinated is one of the most important and effective steps in protecting yourself and others against COVID-19.
If you have questions or concerns about COVID-19, download the Carbon Health app or visit carbonhealth.com to make a virtual or in-person appointment with a healthcare provider.
Carbon Health’s medical content is reviewed and approved by healthcare professionals before it is published. But note that our knowledge and understanding of COVID-19 are developing and changing very rapidly; if you have questions or concerns about COVID-19 precautions, treatments, and vaccinations, please talk to your healthcare provider.
