COVID-19 Reactivates Dormant Viruses in Half of Hospitalized Patients, Nature Study Finds

A large longitudinal study published this week in Nature adds meaningful weight to a hypothesis that's been circulating in the long COVID field: dormant viruses already living in the body may be part of what goes wrong after a severe SARS-CoV-2 infection.

<cite index="11-10">Leveraging multi-omic longitudinal data from 1,154 hospitalized COVID-19 patients enrolled in the Immunophenotyping Assessment in a COVID-19 Cohort (IMPACC) study, the authors found significant reactivation of both Herpesviridae and Anelloviridae during acute disease, with distinct temporal dynamics for different viruses, and showed that reactivation correlates with disease severity, host immune effects, and clinical outcomes.</cite>

The sample size and data depth here are worth pausing on. <cite index="14-6">The IMPACC study collected more than 200,000 samples and generated more than one billion data points over the course of a year across the enrolled patients.</cite> That's not a small convenience cohort you can wave away.

<cite index="13-7,13-8">Nearly half of the participants experienced reactivation of common viruses lurking in their bodies, including herpesviruses such as cytomegalovirus and Epstein-Barr virus, as well as anelloviruses, which are typically harmless and don't cause symptoms.</cite> <cite index="13-9">More than 90% of the global adult population has been infected with at least one of these pathogens.</cite>

The reactivation didn't happen all at once. <cite index="16-5,16-6,16-7,16-8">The viruses did not reactivate simultaneously: Epstein-Barr virus activity was most common near the time patients were admitted, with detectable viral material in 24% of participants during the first eight days before gradually declining, while anellovirus activity was also common early in hospitalization and remained relatively steady until about day 20.</cite>

The long COVID angle is where this paper gets most interesting, and also where the limits of the design show up clearly. <cite index="16-9,16-10">Anelloviruses were of particular interest because their activity after hospitalization was associated with physical problems reported by patients with long COVID, including fatigue and reduced physical function, and this association remained after the researchers accounted for factors including age, medication-related immune suppression, and the severity of the initial infection.</cite>

But the authors are careful not to overclaim. <cite index="12-1">The study does not prove that viral reactivation causes long COVID; it provides evidence that dormant viruses may contribute and could help researchers better understand and eventually treat the condition.</cite> Correlation surviving covariate adjustment is not mechanism. The IMPACC dataset wasn't designed to isolate anelloviral reactivation as an independent variable, and the long COVID phenotyping here relies on patient-reported physical deficits rather than a standardized clinical case definition.

Notably, <cite index="16-12">the study did not find that Epstein-Barr virus activity during acute COVID-19 was more common among patients who later developed long COVID</cite>, which complicates simpler narratives about EBV being a primary driver.

<cite index="10-16">The findings challenge the prevailing view that chronic viral reactivation occurs primarily in immunosuppressed individuals and could inform future approaches to prognostication and treatment.</cite> That's a meaningful conceptual shift. If immunocompetent people are routinely experiencing this during severe infection, the clinical community may have been underestimating how often it happens.

<cite index="13-6">If further research reveals that reactivated viruses can cause people to become seriously ill, it could open the door to new treatments for COVID-19 and even long COVID, says Esther Melamed, a physician-scientist who studies neuroimmunology at the University of Texas at Austin and a co-author of the analysis.</cite> <cite index="16-13,16-14">Researchers said the findings could eventually support new methods of predicting or treating severe COVID-19 and long COVID, including monitoring patients for the reactivation of latent viruses, though existing antivirals for some herpesviruses would still require clinical trials before any treatment application.</cite>

The paper, authored by Cole Maguire, Jing Chen, Nadine Rouphael, and colleagues, appears as "Virus reactivation in acute and long COVID-19" in Nature (DOI: 10.1038/s41586-026-10740-z). The next step the field needs is a prospective trial that actually tests antiviral intervention timed to reactivation windows. Until that exists, this is a well-powered association study pointing in a direction worth following.

Sources cited:
- Nature (Maguire et al., 2026) (https://www.nature.com/articles/s41586-026-10740-z)
- Nature News (https://www.nature.com/articles/d41586-026-02443-2)
- Dell Medical School, UT Austin (https://dellmed.utexas.edu/news/ut-led-study-finds-covid-19-can-awaken-hidden-viruses-throughout-the-body)
- PubMed (IMPACC abstract) (https://pubmed.ncbi.nlm.nih.gov/42557313/)
- News-Medical.net (https://www.news-medical.net/news/20260807/Severe-COVID-19-reactivates-dormant-viruses-and-may-leave-a-lasting-viral-signature.aspx)