Severe COVID-19 cases may trigger the reactivation of several dormant viruses that lie dormant within the human body following prior infections, a new study suggests. Researchers from Boston Children's Hospital, in collaboration with over 20 biomedical research institutions across the U.S. and Canada, investigated this phenomenon by tracking 1,154 hospitalized COVID-19 patients. The study analyzed more than 200,000 biological samples collected over a year.

The research identified 11 distinct dormant viruses that reactivated within the first 40 days after patients were admitted to the hospital for SARS-CoV-2 infection. The findings were published in the journal Nature. Among the reactivated viruses were several herpes viruses, such as Epstein-Barr virus, cytomegalovirus, and herpes simplex virus-1, as well as Anelloviridae, a viral family for which no human disease has been proven.

These viruses are commonly found in a latent state in healthy individuals but can be roused during periods of illness or significant stress. The study specifically noted that the reactivation of Anelloviridae, a virus carried by the majority of adults, was associated with persistent physical disability and the development of long COVID, a condition characterized by lingering symptoms at least four weeks post-infection.

Furthermore, the researchers observed that Epstein-Barr virus and cytomegalovirus appeared to reactivate as a response to inflammation, rather than immune suppression. This suggests a potentially novel mechanism for viral reactivation occurring during severe illness, which was previously not understood to this extent.

Dr. Ofer Levy, a co-author of the study and director of the Precision Vaccines Program at Boston Children's Hospital, expressed surprise at the findings. He stated that the detailed scale of how viral reactivation might be linked to COVID-19 severity and patient outcomes was not previously known.

These revelations could offer valuable insights for understanding long COVID and could aid in the development of future diagnostic tools and therapeutic interventions. However, the study's authors caution that because the research focused exclusively on hospitalized patients with severe COVID-19, the conclusions may not be generalizable to individuals with mild or moderate infections.

While the study established an association between viral reactivation and severe COVID-19, it did not definitively prove that these reactivated viruses are the direct cause of long COVID or long-term disability. Further research is necessary to explore this causal link.

Dr. William Schaffner, a professor of preventive medicine at Vanderbilt University Medical Center who was involved in the study, commented that the research raises more questions than it answers. He emphasized the need for additional studies to determine the significance of these findings, noting that the authors deliberately avoided attributing any specific disease, including long COVID, directly to the reactivated viruses.