Many people ask themselves the same question after contracting the virus: Why did this have to happen to me?"
While some recover quickly, others experience symptoms for weeks or months. Long-term effects of the virus, or "long-haul" symptoms, can take many different forms and even affect people who were previously healthy. There is no simple answer to this question yet.
There is no clear cause
Long-term effects of the virus do not present a uniform clinical picture. Symptoms range from fatigue and cognitive impairment to physical intolerance to exertion. Because these symptoms vary greatly from person to person, it is difficult to define clear risk profiles.
However, research shows that certain factors may be associated with an increased risk of persistent symptoms. These factors do not fully explain the risk, nor do they offer protection against it.
What has been observed so far
A recurring finding in studies is that the course of the acute infection may play a role. Those who experienced a severe case of the disease or required hospitalization, especially in an intensive care unit, are more likely to develop long-term symptoms. Possible causes under discussion include severe inflammatory reactions and physical stress during the acute phase.
It is important to note that a severe course of the disease is not a prerequisite; even mild or initially harmless-seeming infections can lead to long COVID. This makes it difficult to identify clear risk factors and underlying triggers of the condition.
The number of symptoms experienced during the initial infection also appears to be relevant. Studies have found an increased risk associated with the early onset of many different symptoms.
Age, gender, and baseline health status
Several reviews suggest that older age is associated with an increased risk of long COVID. A greater number of preexisting conditions and physical frailty are also described as potential risk factors.
Furthermore, statistical analyses show that women are affected more frequently than men. The reasons for this are not yet conclusively determined. Among other things, biological differences in the immune system, as well as differences in how symptoms are perceived and documented, are being discussed.
Preexisting conditions as a potential influencing factor
Certain underlying health conditions also appear to play a role. These include metabolic disorders, such as diabetes mellitus and obesity; cardiovascular diseases; and chronic respiratory diseases.
These factors can place greater overall strain on the body and influence its response to infection. However, it is important to note that long COVID can also occur in people with no preexisting conditions who were previously healthy and active.
New findings from research
Many researchers currently believe that long COVID is not caused by a single mechanism. Instead, they are investigating various biological processes that may influence one another.
In particular, research is focused on determining whether components of the virus remain in the body after infection and continue to cause symptoms. Researchers are also investigating whether the infection reactivates dormant viruses that many people already carry, such as the Epstein-Barr virus (EBV). Malfunctioning immune responses, in which the body’s defenses attack healthy tissue, may also play a role. Intensive research into EBV is also underway because the virus is considered a major risk factor for other diseases, such as multiple sclerosis.
It is suspected that these mechanisms may vary in severity among individuals. This could explain why long COVID presents so differently and why no single cause has yet been identified.
One often-overlooked aspect is managing the situation after an infection
In addition to medical factors, discussions have emerged about how managing the illness in its early stages might influence its subsequent course. Many affected individuals report quickly returning to their daily routines after the acute infection, sometimes before their bodies had fully stabilized.
Overexertion can play a role, especially in people who later develop exercise intolerance or post-exertional malaise syndrome (PEM). In these cases, symptoms often worsen after a delay following physical or mental exertion.
Therefore, not only the infection itself, but also the recovery phase, can influence the subsequent course of the disease.
Why has it been so difficult to predict risk
Although important findings have emerged from recent research on Long COVID, many questions remain unanswered. One reason for this is that the term "Long COVID" encompasses a wide range of symptoms and disease courses. Consequently, studies are often only partially comparable with one another.
Various factors have been identified that may be associated with an increased risk of long COVID. However, none of these factors can reliably explain why some people develop long-term symptoms after an infection while others do not. Even people without known risk factors can be affected.
For those affected, this means one thing above all else: based on current knowledge, Long COVID cannot be attributed to a single cause or a person’s individual behavior. Rather, it appears that a multitude of biological factors interact in ways that are not yet fully understood.
