Severe Covid Wakes 11 Dormant Viruses, Nature Study Finds
A study of 1,154 hospitalized patients, published in Nature, found that severe Covid reawakens 11 chronic viruses, with the reactivation of one virus family linked to long Covid.
Researchers from 15 American biomedical institutions published results today, August 5, 2026, in the journal Nature, from a study that followed 1,154 patients hospitalized with Covid-19 across 20 hospitals in the United States. Within the first 40 days after admission, doctors detected the reactivation of 11 chronic viruses, the kind people carry for years without knowing it. The reawakening of one poorly studied virus family turned out to be linked to long term physical disability and to long Covid.
The paper is signed by Esther Melamed and colleagues, under DOI 10.1038/s41586-026-10740-z, and grew out of the IMPACC cohort, made up of patients admitted to hospitals in earlier phases of the pandemic and followed for twelve months afterward. One of the lead investigators was Ofer Levy, MD, director of the Precision Vaccines Program at Boston Children’s Hospital.
These chronic infections usually go unnoticed. The Epstein-Barr virus, cytomegalovirus and herpes viruses stay in the body for life once the immune system beats back the initial infection, then lie dormant without symptoms. In recent years, evidence has been building that links their reactivation to autoimmune disease. The best known example is a 2022 study published in Science, based on a cohort of more than ten million US military recruits, which linked Epstein-Barr virus infection to the later development of multiple sclerosis. The new study does not address that same disease, but it looks at the same mechanism from the other side: what happens to those viruses when the body goes through a severe acute infection.
How Many Samples It Took
The team searched for reactivated viruses through genomic sequencing, since a long suppressed infection sometimes returns when the body is under stress. Joann Diray-Arce, who heads the data processing and analysis unit at the Precision Vaccines Program, described the scale of the work.
This is the largest and most comprehensive biomarker study of Covid-19, in which we followed more than a thousand patients, collected more than 200,000 samples and generated more than a billion data points over the course of a year for this public resource.
The database is open to other research teams, which means the same material will be used to answer questions the authors never asked.
Which Viruses Reawakened
Of the eleven viruses detected, four turned up more often than the rest:
- Epstein-Barr virus
- herpes simplex virus 1
- cytomegalovirus
- viruses from the Anelloviridae family
The last item is also the most interesting. Anelloviridae are a poorly described virus family that persists in latent form in about 90 percent of people and is not linked to any known disease. It was precisely the reactivation of these viruses in these patients that tracked with later physical disability and long Covid.
“This link to long Covid is an interesting finding because millions of people around the world suffer from that chronic condition,” Levy said in a statement from the hospital.
Inflammation, Not a Weakened Immune System
Analysis of the blood samples produced a finding that departs from the prevailing explanation. The assumption had been that dormant viruses reawaken once the immune system weakens. Here, the Epstein-Barr virus and cytomegalovirus reactivated alongside systemic inflammation, in people whose immunity had not been suppressed. The authors describe this as a previously unknown mechanism.
Levy also points to why the topic is not closed.
Although many people no longer consider Covid a problem, up to 50,000 people died of Covid in the United States during the 2025/2026 respiratory season, and by some estimates more than ten million American adults suffer from long Covid.
Is It Proven That Viruses Cause Long Covid?
No. The study measures association, not causation. The finding that one virus family reactivated more often in patients who later developed long Covid leaves at least three explanations open: that viral reactivation contributes to the symptoms, that it is simply a byproduct of the same severe disease course that leads to long Covid, or that both findings stem from some third factor that was not measured.
The sample itself carries limitations too. Only hospitalized patients, meaning more severe cases, were followed, so the results do not extend to people who went through Covid at home. The findings cover only the first 40 days after admission, not an arbitrary point after infection. No therapy was tested here, and nothing shows that preventing viral reactivation would change outcomes. The next step the team has announced points in exactly that direction, toward how the immune system responds to these viruses during illness and when an intervention might actually make sense.
