Severe Covid-19 may 'wake up' dormant viruses in the body, study finds

The findings suggest severe Covid-19 could alter the body's existing viral environment, although further research is needed to understand the impact

  A severe Covid-19 infection may open the door for other viruses already hiding in the body. A new study found evidence that several dormant viruses can become active during severe infection, offering fresh clues about the complex biological changes triggered by Covid-19.

 

The study, published in the journal Nature last week, found evidence of reactivation involving multiple chronic viruses in hospitalised Covid-19 patients. Researchers also detected some viral activity after the acute infection had passed, raising questions about how these changes could influence recovery.

 

What did the study find?

 

The study, titled “Virus reactivation in acute and long Covid-19,” analysed data from 1,154 people who had been hospitalised. The patients were part of a research project called the Immunophenotyping Assessment in a Covid-19 Cohort (IMPACC).

 

Researchers monitored them during their illness and continued to track their health for up to 12 months after they recovered. They examined blood, nasal swabs and, where available, samples from the airways of mechanically ventilated patients. They used RNA sequencing and other techniques to look for signs that viruses were actively replicating in the body. This differed from simply checking for antibodies, which can show that a person had been infected by a virus in the past.

 

They detected reactivation of viruses from the Herpesviridae and Anelloviridae families, including:

 

• Epstein-Barr virus (EBV)
• Cytomegalovirus (CMV)
• Herpes simplex virus 1 (HSV-1)
• Herpes simplex virus 2 (HSV-2)
• Human herpesvirus 6 (HHV-6)
• Several Anelloviridae viruses

 

The researchers found that viral activity varied depending on the virus. EBV tended to reactivate early in the illness, while CMV and HSV-1 were more commonly detected later and particularly in respiratory samples.

 

Why do dormant viruses reactivate?

 

Many people carry viruses that remain in the body after the initial infection but are normally kept under control by the immune system. These viruses can become active again when the body experiences major stress, including critical illness.

 

The new findings suggest that severe Covid-19 may create conditions that allow some of these viruses to become active even in people who are not obviously immunosuppressed. Importantly, the researchers found that reactivation was associated with increased inflammation, rather than simply being explained by weakened immunity.

 

This could help explain why several viruses appear to reactivate during severe infections, although the study does not establish that these viruses directly cause Covid-19 complications.

 

Could viral reactivation be linked to long Covid-19?

 

The researchers did not find a clear link between viral reactivation during the initial infection and the different groups of long Covid-19 symptoms they studied. They stressed that the findings do not prove that reactivated viruses cause long Covid-19.

 

The researchers said viral reactivation may potentially amplify inflammation and contribute to some clinical outcomes, but further studies are needed to determine whether it is a cause of complications or simply a consequence of severe illness.

 

The study also has some limitations, as it looked at unvaccinated patients hospitalised with Covid-19 who were mainly infected with early SARS-CoV-2 strains. It is therefore unclear whether the same pattern would be seen in vaccinated people, those infected with newer variants, or people with milder Covid-19.