Long-COVID Symptoms Are Common—Even After Mild or Asymptomatic Cases, New Study Shows

Scientists are working to understand the array of lingering symptoms or new health conditions that may start weeks after a COVID-19 infection (sometimes termed long COVID, long-haul COVID, or post-acute COVID-19 syndrome). A huge new study published this week adds to a growing pile of research indicating that it is surprisingly common for people to experience new health problems after a COVID-19 infection. And the results suggest this can happen even among those who had mild-to-moderate or no symptoms during their illness.

FAIR Health, a nonprofit organization that amasses data on health insurance claims in the U.S., conducted a study analyzing the insurance records of over 1.9 million COVID-19 patients between February 2020 and February 2021. The records showed that 23.2% of the COVID-19 patients (about 454,000 people) visited a health care provider for a new health concern, for the first time, a minimum of 30 days after their COVID-19 diagnosis. 

The researchers filtered the records to look for 38 different diagnostic codes (selected based on FAIR Health’s insurance data and the work of other researchers) representing a wide variety of symptoms and conditions, including anemia, anxiety, blood clots, cognitive impairment (brain fog), depression, diabetes, gastroesophageal reflux disease (GERD), hypertension, migraine or headache, pain, respiratory distress, skin issues, and swallowing difficulties. To account for the possibility that someone was seeking treatment for an underlying medical problem that predated their COVID-19 infection, patients who had previously sought care for that particular condition were excluded from the study (along with all patients with certain co-morbid conditions, like cancer or stroke). 

As expected based on previous research, post-COVID symptoms and conditions were much more common following more severe cases of the virus. In fact, half of the individuals who were hospitalized for COVID-19 experienced those issues. On top of that, though, a high number of people with less serious (or unnoticeable) cases also sought medical care for new health issues a month or more post-diagnosis. 

For instance, 27.5% of people who experienced symptoms but were not hospitalized later presented with a new health issue. And among individuals who had no COVID-19 symptoms during their infection (55% of all the patients in the study), 19% saw a provider for a new health concern at least 30 days later. (Interestingly, not a single one of the patients whose only symptom was loss of taste or smell presented with a long-term or lingering health issue.) 

The most common issue across all age groups was pain, which occurred in 5% of patients at least one month after their diagnosis. (This included a number of different diagnoses, like nerve pain or inflammation and muscle pain.) Next were breathing difficulties, like shortness of breath (affecting 3.5% of patients); hyperlipidemia, or high levels of triglycerides or cholesterol in the blood (3%); malaise and fatigue (2.9%); and hypertension (2.4%). The following most common conditions were anxiety, intestinal issues, skin issues; high blood sugar levels, cholesterol, or blood pressure; and abnormal heart results. 

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Most of the conditions were more likely to occur in people identified as female than male in insurance records, and the prevalence of different conditions changed across age groups. The prevalence of mental health issues, for example, varied particularly widely: Females were over twice as likely as males to seek help for anxiety and depression, while anxiety was the second-most common condition in people ages 19 to 29. 

The majority of people who get COVID-19 will recover just fine. But a significant number of people suffer long after the acute phase of their infection has passed, although there are varied estimates about how common long COVID is in general. This new study, which has not been peer-reviewed but includes data on the largest population of COVID-19 patients studied for long-term health effects to date, only strengthens that evidence. It also makes the case that even people with mild, moderate, or no symptoms may be affected. “The strength of this study is really its size and its ability to look across the range of disease severity in a diversity of age groups,” Helen Chu, M.D., an associate professor of medicine and infectious diseases at the University of Washington School of Medicine (who did not work on the paper), told the New York Times. 

Still, researchers have a lot of unanswered questions about the long-term effects of COVID-19. For instance, like previous studies, this one couldn’t definitively establish that COVID-19 directly caused the health conditions people in the study developed later. (The authors of the FAIR Health study point out that in the case of hyperlipidemia and hypertension, for instance, it is possible that people already had these conditions before they got COVID-19 but were unaware.)

Researchers also have yet to understand the potential mechanisms underpinning such a wide variety of health issues across so many different bodily systems (including the metabolic, cardiac, and nervous systems), even in individuals who weren’t seriously sick. And the best treatment option for any particular patient isn’t totally clear, either. But treatment typically depends on the condition they are dealing with and can include managing symptoms and support groups.

Fortunately, researchers at private and public institutions, like the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) are taking long COVID seriously and putting resources toward better understanding it. A number of studies are currently under way, according to the CDC. And with more time and research, the hope is that we can better anticipate, identify, prevent, manage, and treat the potential long-term health effects of COVID-19. For now, as the CDC notes, the most effective way to handle post-COVID-19 complications is to prevent infection in the first place through vaccination and public health measures.