Can Asymptomatic COVID Infections Result in Long COVID?

Yes, it's possible for anyone who contracted COVID-19 to experience a wide range of ongoing health problems as a result of their infection, even those who did not experience any symptoms or had a mild illness. However, experts say this phenomenon, known as long COVID, tends to occur more often among individuals who had a severe illness.

There is still much to know about the mechanism of long COVID, but further research is expected to shed more light on the matter.

One of the largest long COVID studies to date recently reported that asymptomatic SARS-CoV-2 infections are generally not linked to long COVID. To determine the frequency, nature, and impact of long COVID in the general population, the researchers studied more than 33,000 confirmed cases of COVID-19 with almost 63,000 never-infected individuals and conducted regular follow-ups. Their findings are published in Nature Communications.

Although it may be reassuring that the study did not find asymptomatic infections to be associated with any long-term health impacts, experts said you're not totally out of the woods if you had no symptoms.

Why Are Some Individuals Asymptomatic?

The symptoms of a viral infection are directly related to the body’s immune response to fight it off. This immune response includes a variety of inflammatory pathways that can destroy the virus but also irritate the body’s cells, organs, and tissues, Mark Loafman, MD, MPH, a family physician and chair of the Family and Community Medicine Department at Cook County Health, told Verywell.

It may help to consider the wide range of immune responses to a mosquito bite. Some people develop a large and intensely itchy hive, while others have little to no reaction at all, Loafman added. 

The same goes for COVID-19. For some, the immune response is mild to the extent that it does not cause any symptoms. Many people develop symptoms that last about a week, but others experience a dysregulation in their immune system that prolongs the time frame by weeks or even months.

The range of immune response—from mild to severe—is based on many different factors. According to Irfan Hafiz, MD, infectious disease physician and chief medical officer at Northwestern Medicine Regional Medical Group, these factors include the following:

• Genetics and age of the host
• Comorbidities of the host
• Viral factors, like the strain
• Previous immunity from either past infection or vaccination
• Viral inoculum, or the extent of exposure to the virus

There's no single factor to predict whether a person will have a mild or a severe infection, Hafiz told Verywell.

Are Asymptomatic Cases Risk-Free?

The study found that long-term impacts of COVID-19 were more likely to occur after severe infections that required hospitalization and in older, female patients with pre-existing health problems.

Based on their findings, the authors also reported that they “found no evidence of sequelae following asymptomatic infection.” However, experts advise against assuming that asymptomatic infections aren’t associated with persistent symptoms at all.

Long COVID may be less likely among asymptomatic people, but the risk is probably not zero, Hafiz said. According to a 2021 Pathogens study, post-COVID symptoms develop among 30% to 60% of patients who had either asymptomatic or mild COVID-19 infections. Most of the time, it occurred among women.

“While the odds of zero harm from an asymptomatic infection are very good, there is some risk of serious illness after the infection resolves,” Loafman said. Aside from persistent symptoms, people may also experience post-viral illnesses that develop in response to the initially asymptomatic viral infection. Post-viral syndrome can range from a mild rash to cardiac dysfunction or paralysis, he added.

Vaccination against COVID-19 may reduce the risk of some persistent symptoms, which is extremely beneficial. The risk of post-viral illnesses is one of the many reasons why public health measures place a big emphasis on vaccination when limiting the spread of infection, Loafman said. 

The vaccine helps the body’s immune response behave in a more functional, routine manner.

"The data on COVID vaccination—and we have a ton of it now—continues to be simply overwhelmingly favorable, with no real downside," he added.

How Does Long COVID Affect the Quality of Life?

Aside from the fact that asymptomatic infections can still cause persistent symptoms, it’s also important to point out that some people with long COVID got worse over time and didn’t improve.

"There are a lot of people who have gotten worse over the years, not better," Hannah Davis, co-founder of the Patient-Led Research Collaborative, told Verywell. "About half of long COVID cases are ME/CFS and/or dysautonomia, which are both extremely debilitating, lifelong conditions. ME/CFS is considered the most debilitating non-fatal illness, with a quality of life worse than end stage renal failure."

According to the Nature Communications study, about 42% of people who had symptomatic COVID-19 feel only partially recovered between six and 18 months after their initial infection. This detail about partial recovery demonstrates that there is a spectrum of illnesses.

"Even if they can work and do basic life activities, COVID has decreased the quality of life for millions of people," Davis said.

Overall, the risk of long COVID is never zero, no matter whether you’ve had a mild or severe illness. You must continue practicing public health measures because reinfection may prolong or worsen long COVID symptoms.

"Long COVID is happening more and more in people who are fully vaccinated and boosted and even in people who had COVID earlier and recovered fine," Davis said. "The only current way to prevent long COVID is to prevent COVID. Vaccination is not a sufficient replacement for masks and other safety measures."

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.