COVID-19 may leave behind more than the memory of an infection. A large new study suggests that when the illness becomes severe, it can disturb viruses that have been quietly living in the body for years. These viruses are not necessarily new infections. Some, including Epstein-Barr virus, cytomegalovirus (CMV), and herpes simplex virus, can remain in the body after an earlier infection and stay under control for long periods. Researchers now have evidence that severe COVID-19 can coincide with these viruses becoming active again, raising new questions about what happens inside the body during and after a serious infection.
The findings come from an unusually large study of 1,154 people hospitalized with COVID-19, followed through extensive biological testing. Researchers examined more than 200,000 samples and generated more than 1 billion data points, allowing them to track viral activity over time rather than relying on a single blood test. Nearly half of the participants showed evidence of at least one dormant virus becoming active during their illness. The findings are especially interesting for people who continue to experience problems after COVID-19, because some of the viral signals persisted during recovery and were associated with lasting symptoms. Still, the study does not prove that these reactivated viruses cause long COVID, and that distinction matters.
Severe COVID-19 Can Stir Up Viruses Already Inside You
When you think about a viral infection, you may picture one virus entering the body, multiplying and then being cleared by the immune system. Human biology can be more complicated. Several viruses can remain in the body after an earlier infection, sometimes for decades, without causing obvious symptoms. The immune system normally keeps these viruses under control. Epstein-Barr virus, for example, commonly remains in the body after the initial infection, while herpesviruses can also establish long-term infections.
The new research, published in Nature in August 2026, looked at what happened to these viruses during severe COVID-19. Researchers analyzed patients enrolled in the Immunophenotyping Assessment in a COVID-19 Cohort study, or IMPACC, across 20 U.S. biomedical research hospitals. Participants were enrolled between May 2020 and March 2021, when vaccines were not yet widely available. This gave researchers an opportunity to examine people whose immune systems were encountering SARS-CoV-2 without the protection provided by prior vaccination.
Within the first 40 days after hospital admission, the researchers detected activity from 11 different viruses that had previously been quiet. Epstein-Barr virus, herpes simplex virus-1 and cytomegalovirus were among the better-known viruses identified. The study also found activity involving Anelloviridae, a large family of viruses that can be found in most people but is generally less familiar to the public.
What makes the findings particularly interesting is that reactivation was not restricted to people who were already known to have severely weakened immune systems. The researchers found evidence of viral reactivation in people who were considered immunocompetent. This suggests that the intense biological stress of severe COVID-19 may alter the balance between the immune system and viruses that have been kept quiet.
Inflammation May Be Part of the Trigger
For years, doctors have known that certain dormant viruses can become active when the immune system is significantly suppressed. This can happen with some cancers, transplant medications and other conditions that interfere with immune defenses. The new study points toward another possibility: severe inflammation itself may be associated with viral reactivation.
The researchers found that viral activity tended to increase alongside markers of inflammation and disease severity. In other words, the people whose bodies were experiencing a stronger inflammatory response were more likely to show evidence that chronic viruses had become active. This pattern was seen even among patients who were not taking medications designed to suppress the immune system.
That does not mean inflammation has been proven to directly wake up every dormant virus. The human immune system is an enormous network of cells, proteins and chemical signals, and the study cannot isolate every step that connects severe SARS-CoV-2 infection with viral reactivation. It does, however, suggest that the body’s response to the infection may be just as relevant as the virus itself when researchers try to understand what happens during severe disease.
This distinction may help explain why COVID-19 can produce such different experiences from one person to another. Two people can become infected with the same virus but have very different immune responses. Age, previous infections, underlying health conditions and other biological factors can influence how the body responds. The new findings add dormant viruses to the list of factors researchers may want to examine when studying severe COVID-19 and recovery.
The Quiet Surprise: Anelloviruses and Long COVID
Epstein-Barr virus received much of the attention in discussions about viral reactivation and long COVID, but the study also drew attention to a much less familiar group: Anelloviridae. These viruses are extremely common, and many people carry them without knowing it. Their presence has generally been difficult to interpret because detecting anellovirus does not automatically mean that a person is sick.
In this study, however, persistent anellovirus activity during recovery was associated with lasting physical problems. Researchers found that anellovirus signals were more common among patients who continued to experience fatigue and reduced physical function. This does not establish that anelloviruses are responsible for those symptoms, but it gives scientists something measurable to investigate.
That matters because long COVID can be difficult to diagnose using a single laboratory test. People may experience exhaustion, difficulty concentrating, shortness of breath, sleep problems or reduced exercise tolerance even after the original infection has passed. Researchers have been searching for biological markers that could help distinguish people who recover quickly from those who develop prolonged symptoms.
The new findings do not provide that diagnostic test yet. Instead, they offer another potential piece of the puzzle. If future research confirms that certain patterns of viral reactivation consistently appear in people with long COVID, those patterns could eventually help researchers understand why recovery takes longer for some people. For now, the evidence is promising enough to study but not strong enough to support treating viral reactivation as the established cause of long COVID.
What the Study Says About Severe Illness
The researchers also found connections between viral reactivation and clinical outcomes during severe COVID-19. Some forms of CMV activity in the respiratory tract were associated with a higher risk of complications, while Epstein-Barr virus detected in the nasal cavity was associated with increased risk of death within a year. Other viral signals were associated with problems involving the lungs, bloodstream, kidneys, blood vessels and nervous system.
These associations became more noticeable as COVID-19 became more severe. Patients with the most serious illness also tended to have longer hospital stays, with the most severely affected group spending more than 28 days in the hospital. The findings therefore suggest that viral reactivation may serve as a marker of how much stress the body is experiencing during a serious infection.
There is another possibility researchers will need to examine. Viral reactivation could contribute to complications, but it could also be a consequence of the severe illness itself. A person who is critically ill may experience changes in immune activity, metabolism, inflammation and organ function that create conditions in which dormant viruses become detectable. The reactivation could therefore be part of the disease process, a response to it, or both.
This is why the study should not be interpreted as proof that a dormant virus caused a patient’s complication. The researchers themselves describe the findings as associations rather than evidence of causation. More studies are needed to determine whether suppressing a reactivated virus changes a patient’s outcome.
Why This Does Not Mean You Need Antiviral Treatment
The discovery that dormant viruses can become active during severe COVID-19 may naturally make you wonder whether testing or antiviral treatment should become part of routine care. At this point, the study does not support that conclusion.
Some established laboratory tests can detect several of the viruses examined in the research, and antiviral medications are already available for certain herpes-family infections. Researchers say the next question is whether identifying and treating reactivated viruses can actually improve outcomes. That question can only be answered through carefully designed clinical studies.
It is also important to remember who was included in the research. The study focused on people hospitalized with COVID-19, meaning the findings cannot automatically be applied to everyone who has had a mild infection. A positive test for a dormant virus also does not necessarily mean that the virus is causing symptoms or needs treatment.
If you have persistent symptoms after COVID-19, especially significant fatigue, breathing problems, neurological symptoms or a decline in your ability to function, talk with a healthcare professional rather than trying to diagnose viral reactivation on your own. Persistent symptoms can have many possible causes, and appropriate evaluation should be based on your individual history and symptoms.
What You Can Do While Researchers Keep Looking
Although this study does not establish a specific natural remedy for viral reactivation, it does reinforce a sensible approach to recovery: give your body the conditions it needs to heal while paying attention to symptoms that do not resolve. Recovery from a major infection can take time, and pushing through significant fatigue or other symptoms is not always the best strategy.
Start with the basics. Aim for consistent sleep, regular hydration and nourishing meals that provide adequate protein, fiber, fruits, vegetables and other nutrient-dense foods. These habits do not eliminate dormant viruses, but they support general health while your body recovers. Gentle movement can also be useful when tolerated, although people with post-exertional worsening should discuss activity levels with a healthcare professional rather than forcing themselves through symptoms.
Stress management deserves attention as well. Severe illness can place substantial physical and emotional demands on the body. Practices such as slow breathing, meditation, gentle stretching and time outdoors may help you manage stress and improve your sense of well-being. They should complement medical care, not replace it.
Most importantly, don’t assume that persistent symptoms are simply something you have to live with. If fatigue, brain fog, sleep problems, shortness of breath, pain or reduced physical ability continue after an infection, keep a record of your symptoms and discuss them with your healthcare provider. The new study may eventually lead to better ways of identifying different patterns of post-COVID illness, but there is still much to learn.
The Body May Be Telling a More Complicated Story
The most interesting message from this research may be that COVID-19 is not always a story about SARS-CoV-2 alone. For some people with severe disease, the infection appears to disturb a much larger biological environment, including viruses that were already present in the body. Seeing those viruses become active gives scientists another way to study what happens during severe illness and why some people struggle during recovery.
At the same time, science has not yet answered the most important question: does viral reactivation actually cause some of the problems associated with severe COVID-19 or long COVID? This study cannot answer that by itself. The researchers have identified a strong pattern, but future clinical studies will need to determine whether changing that pattern changes how patients feel and recover.
For now, the findings offer a reason to take persistent post-COVID symptoms seriously without jumping to conclusions about their cause. Your body is not simply switching an infection on and off. Immune activity, inflammation, previous infections and many other biological processes can overlap during illness. As researchers continue studying these connections, the hope is that a better understanding of what happens inside the body will eventually lead to more precise ways of identifying and treating people who do not fully recover after COVID-19.
Sources:
- Severe COVID may awaken dormant viruses, leading to autoimmune disease, long COVID. (2026, August 6). CIDRAP. https://www.cidrap.umn.edu/covid-19/severe-covid-may-awaken-dormant-viruses-leading-autoimmune-disease-long-covid
- Maguire, C., Chen, J., Rouphael, N., Morse, B. A., Hoch, A., Pickering, H., Van Phan, H., Glascock, A., Chu, V., Dandekar, R., Network, I., Holland, S. M., Rosen, L. B., Lee, S., Vaysman, T., Diray-Arce, J., Chen, J., Kho, A. T., Milliren, C. E., . . . Melamed, E. (2026). Virus reactivation in acute and long COVID-19. Nature. https://doi.org/10.1038/s41586-026-10740-z
- Study finds COVID-19 can reactivate dormant viruses | AHA News. (2026, August 7). American Hospital Association | AHA News. https://www.aha.org/news/headline/2026-08-07-study-finds-covid-19-can-reactivate-dormant-viruses
