Researchers with the IMPACC study analyzed more than 200,000 samples from 1,154 patients hospitalized with COVID-19 across 20 U.S. hospitals, looking for latent viruses that reactivated during acute illness. Within 40 days of admission they detected 11 reactivated viruses, most commonly Epstein-Barr virus, herpes simplex virus 1, cytomegalovirus, and the poorly understood Anelloviridae family.
Reactivation of Anelloviridae was associated with long-term physical disability and long COVID, offering a possible molecular thread to pull on in a condition that has resisted biological explanation. The team also found that Epstein-Barr and cytomegalovirus reactivation correlated with systemic inflammation rather than immunosuppression alone, meaning it can happen in people whose immune systems are otherwise healthy.
The authors caution that these associations do not establish causation.