HEALTH
You probably think you got over your last case of chickenpox, that mono you had in college, or the cold sore virus you picked up from a childhood kiss. You didn't. Those viruses never left. They went to sleep, tucked away in your nerve cells and white blood cells, waiting.
Now, a sweeping new study published in the journal Nature has confirmed one of the more unsettling twists of the COVID-19 era: a severe case of the virus can reach into that sleeping arsenal and shake it awake. Herpes viruses, a mysterious and little-understood family called Anelloviridae, and other long-dormant infections roar back to life inside hospitalized COVID patients — and the reactivation of one particular virus family tracks disturbingly closely with who goes on to develop long COVID.
It is, researchers say, a discovery that reframes what a "COVID infection" actually is. It isn't just a fight against one virus. For the sickest patients, it may be a fight against an entire hidden viral underworld getting kicked back into gear.
An Unprecedented Look Inside 1,154 Hospitalized Patients
The research, led by scientists at the University of Texas at Austin working with Boston Children's Hospital and more than a dozen other biomedical institutions across the country, is the product of the National Institutes of Health-funded IMPACC study — Immunophenotyping Assessment in a COVID-19 Cohort. Between May 2020 and March 2021, researchers tracked 1,154 hospitalized, unvaccinated COVID-19 patients across 20 U.S. hospitals, collecting more than 1 billion data points from over 200,000 nasal swabs, blood draws, and endotracheal aspirates.
What made this study different from prior work is precision. Instead of testing for antibodies — the blunt instrument doctors typically use to see if a person has ever been exposed to a virus — the team hunted for RNA, the genetic signature of viruses that are actively, currently replicating inside the body right now. That distinction matters enormously. Antibodies tell you a virus visited once, years ago. Actively replicating RNA tells you a virus is awake and multiplying today.
The results, published this month, are striking: RNA from 11 different dormant viruses turned up reactivated in patients within the first 40 days after hospital admission. The most common were herpes simplex virus 1 (the cold sore virus) and the Anelloviridae family, followed by Epstein-Barr virus, cytomegalovirus (CMV), and assorted enteroviruses.
"Viruses use diverse strategies to enhance their persistence and dissemination, including establishing chronic infection," the study authors wrote. "Chronic viral infections are ubiquitous in humans, with individuals carrying multiple viruses that can reactivate during physiological stress, including severe illness."
To put that in plain English: nearly everyone is walking around as a carrier hotel for old infections. Most people harbor somewhere between eight and twelve of these dormant viruses at any given moment without ever knowing it. Normally your immune system keeps them locked in a cage. Severe COVID, it turns out, can rattle that cage loose.
The Virus Nobody's Heard Of — and Why It Might Explain Long COVID
Of all 11 reactivated viruses identified, the one drawing the most attention from scientists is the one almost nobody outside a virology lab has ever heard of: Anelloviridae.
It's a strange, poorly understood viral family that lives dormant in roughly 90% of the human population, generally causing no known disease on its own. Scientists have struggled for years to figure out what, if anything, it actually does inside the body. This study may have just found its smoking gun.
Reactivation of Anelloviridae was strongly and specifically tied to long COVID and long-term physical disability in the study's patients. Unlike Epstein-Barr virus, which spiked early after hospital admission and then faded, Anelloviridae behaved differently — its viral RNA levels stayed elevated and steady for roughly three weeks before slowly declining, a pattern that lines up unnervingly well with the drawn-out, months-long course that long COVID patients describe.
Researchers estimate more than 10 million American adults currently suffer from long COVID, a condition still without a definitive diagnostic test, an agreed-upon cause, or an approved treatment. For years, patients navigating brain fog, crushing fatigue, and cardiovascular symptoms months after their initial infection cleared have been told, in effect, that doctors don't fully know what's wrong with them. This study offers the first concrete biological fingerprint that might explain at least part of it.
Inflammation, Not a Weak Immune System, May Be the Real Trigger
Perhaps the most scientifically surprising finding buried in the data upends a longstanding assumption about how viral reactivation works.
The conventional wisdom in medicine has long held that dormant viruses reawaken specifically when the immune system is suppressed or weakened — think of how shingles (a reactivation of the chickenpox virus) tends to strike older adults or people on immune-suppressing medications. Doctors assumed COVID-triggered reactivations worked the same way: the virus knocks your immune system down, and old infections seize the opportunity.
This study says that's not the whole story, at least for Epstein-Barr virus and cytomegalovirus. Instead, the data show these two herpesviruses reactivated in step with rising systemic inflammation — not with markers of immune suppression. In other words, it may be the body's own inflammatory firestorm, the same runaway immune response that puts COVID patients on ventilators, that's shaking these dormant viruses loose, rather than a weakened immune system failing to hold them down.
"The disease probably induces the stress that triggers the reactivations, and then these reactivations further amplify the inflammation," researchers explained — describing what looks like a vicious feedback loop: COVID causes inflammation, inflammation wakes old viruses, and those newly reactivated viruses pour fuel back onto the inflammatory fire.
That loop may help explain why the sickest COVID patients so often spiral into complications that seem to go beyond the original infection. The study found that patients with detectable CMV in their nasal cavity were more likely to develop a collapsed lung (pneumothorax), while CMV detected in blood cells was linked to bloodstream infections, kidney complications, stroke, pulmonary vascular disease, and shock. Patients with CMV in the respiratory tract or EBV in the nasal cavity when severely ill were also more likely to die within a year.
"We Need to Help These Patients Recover"
Dr. Ofer Levy, a physician-scientist and director of the Precision Vaccines Program at Boston Children's Hospital, served as a site principal investigator on the study. He doesn't mince words about why this research still matters in 2026, four years after the worst of the pandemic receded from headlines.
"Although many no longer think of COVID being a problem, up to 50,000 Americans died of COVID in [the] 2025–2026 respiratory season and some estimates suggest over 10 million U.S. adults suffer from long COVID," Levy said in a statement accompanying the study's release. "We need to help these patients recover with the best outcomes."
Levy also flagged the study's relevance well beyond COVID itself. "Sooner or later, there may be another coronavirus pandemic, which means we need to learn all the lessons we can from COVID-19 to be better prepared," he said.
Notably, the researchers stop short of claiming they've proven that viral reactivation directly causes worse outcomes or long COVID — this is an observational study, showing a strong association, not a randomized experiment proving cause and effect. The authors are careful to describe their findings as "immune, transcriptomic and metabolomic signatures of viral reactivation that could inform future strategies to prognosticate and treat acute COVID-19 and long COVID" — a scientific way of saying: this is a map, not yet a cure.
The team's next step is to dig into exactly how the immune system responds to these viruses during a COVID infection, with the goal of identifying ways to prevent reactivation altogether — and figuring out the optimal window in which to intervene with treatment.
What This Means for You
If you or someone you love has been hospitalized with a severe case of COVID-19, this research suggests your body may be fighting a wider battle than just the coronavirus itself — one involving old infections most people don't even know they're carrying. For the millions living with unexplained, lingering symptoms since a COVID infection, this study is among the strongest evidence yet that their symptoms have a measurable, biological basis rooted in viral reactivation, not something imagined or exaggerated.
Practically speaking, this doesn't yet change clinical care. There's no approved test you can walk into a clinic and request for "Anelloviridae reactivation," and no new drug on pharmacy shelves targeting it. But the study strengthens the case for closer monitoring of severely ill COVID patients using existing, already-validated PCR technology that can detect herpesviruses and Anelloviridae — tools hospitals already have on hand. Levy and his colleagues suggest this kind of monitoring could eventually help doctors flag patients at high risk for long-term complications early, rather than waiting for symptoms to spiral for months.
For long COVID patients who have spent years being told their labs "look normal," this research is unlikely to be a cure — but it may be validation. Something measurable really is happening in their bodies. Science is only now catching up to what patients have been reporting for years.
The Bottom Line
COVID-19 was never just a respiratory virus, and this study is the latest reminder of how far its reach can extend. By reactivating a hidden population of dormant infections most of us carry without knowing it, severe COVID appears capable of setting off biological chain reactions that echo long after the initial illness clears. As the researchers themselves warn, there will likely be another pandemic virus someday — and understanding exactly how this one exploited the sleeping infections already inside us may be one of the most important lessons it left behind.
