A study found that the SARS-CoV-2 virus can linger in the lungs of some people for up to 18 months following infection. In most cases, the SARS-CoV-2 virus in the upper respiratory tract goes undetected one to two weeks after contracting COVID.
The study on lung cells in an animal model was carried out by a team from the Institut Pasteur in cooperation with the Alternative Energies and Atomic Energy Commission (CEA), a French public research institute.
The findings, which were published in the journal Nature Immunology, demonstrate that SARS-CoV-2 can remain in the lungs of some people for up to 18 months following infection. Furthermore, the virus’s persistence seems to be connected to a breakdown in innate immunity, the body’s first line of defense against infections.
After causing an infection, some viruses quietly and imperceptibly continue to exist in the body. The researchers claimed that they continue to exist in “viral reservoirs.”
This is the case with HIV, which can reactivate at any time and is latent in specific immune cells. They said that the SARS-CoV-2 virus, which causes COVID-19, might also be the culprit.
“We found that after primates contracted SARS-CoV-2, inflammation lingered for extended periods of time. Thus, we surmised that it might be caused by the virus existing within the body “, stated Michaela Muller-Trutwin, Head of the HIV, Inflammation and Persistence Unit at the Institut Pasteur.
Biological samples from virus-infected animal models were analyzed for the study.
According to preliminary study findings, some people had viruses discovered in their lungs six to eighteen months after infection, despite the fact that the virus was not detectable in the blood or upper respiratory tract.
Additionally, the researchers discovered that compared to the original SARS-CoV-2 strain, the Omicron strain had less persistent virus in the lungs.
“We were really surprised to find viruses in certain immune cells – alveolar macrophages – after such a long period and when regular PCR tests were negative,” said Nicolas Huot, the study’s first author and an investigator in the HIV, Inflammation and Persistence Unit at the Institut Pasteur.
“What’s more, we cultured these viruses and were able to observe, using the tools we developed to study HIV, that they were still capable of replicating,” Huot stated.
The researchers then focused on natural killer (NK) cells to learn more about the function of innate immunity in managing these viral reservoirs.
“The cellular response of innate immunity, which is the body’s first line of defense, has been little studied in SARS-CoV-2 infections until now,” stated Muller-Trutwin.
“Yet it has long been known that NK cells play an important role in controlling viral infections,” said the investigator.
According to the study, SARS-CoV-2-infected macrophages can develop resistance to NK cell destruction in certain animals, but in other animals, NK cells can adapt to the infection and kill resistant cells—in this case, macrophages—as long as they are present.
A mechanism that could account for the existence of viral reservoirs is clarified by the study.
The researchers also found that while people with low or no long-term virus produced adaptive NK cells, those with higher viral levels not only lacked adaptive NK cells but also showed decreased NK cell activity.