Severe COVID-19 can rouse other viruses lying dormant in the body — and the pattern may help explain the still-mysterious condition known as long COVID, a major new study reports.
Researchers at Boston Children’s Hospital and 15 other U.S. institutions tracked 1,154 COVID-19 patients over a year as part of the IMPACC study, collecting more than 200,000 samples and over a billion data points. They found that severe infection reactivated long-dormant viruses — including Epstein-Barr virus, herpes simplex 1 and cytomegalovirus (11 viruses in all). The work was published August 5, 2026 in Nature.
A surprising trigger
The bigger surprise was the cause. Rather than the reactivation stemming from a weakened immune system, it appeared to be driven by inflammation — the intense, body-wide inflammatory response seen in severe illness — even in people with otherwise healthy immune systems. That reframes how doctors think about why dormant viruses wake up during serious infection.
The long-COVID link
One group of viruses stood out: reactivation of Anelloviridae, a family of very common, usually harmless viruses, was prominently associated with long-term physical disability and long COVID. “This association with long COVID is an interesting finding, as millions around the world suffer from this chronic condition,” said senior author Ofer Levy. The findings are associations, not proof of cause, but they point toward new ways to diagnose and potentially treat long COVID by targeting viral reactivation.