In a study conducted by the Institut Pasteur and the Alternative Energies and Atomic Energy Commission (CEA), researchers have discovered that the SARS-CoV-2 virus, responsible for causing COVID-19, can persist in the lungs for up to 18 months after infection. Published in the esteemed journal Nature Immunology, the study highlights the link between the virus’s long-term presence and a potential failure of the body’s innate immune response.
This study has far-reaching implications for our understanding of COVID-19 and its long-term effects on individuals. The persistence of the virus in the lungs raises concerns about potential health complications and the need for further research to develop effective treatments and preventive measures.
Typically, one to two weeks after contracting COVID-19, the SARS-CoV-2 virus becomes undetectable in the upper respiratory tract. However, the study reveals that certain individuals continue to harbor the virus in their lungs for an extended period. This phenomenon, similar to viral reservoirs observed in infections like HIV, poses significant implications for long-term health.
“We observed persistent inflammation in primates infected with SARS-CoV-2 over extended periods, leading us to suspect the presence of the virus in the body,” explained Michaela Muller-Trutwin, Head of the Institut Pasteur’s HIV, Inflammation, and Persistence Unit.
The study examined biological samples from animal models infected with the virus and found evidence of viral persistence in the lungs, even when undetectable in the upper respiratory tract or blood. Surprisingly, the researchers discovered that the Omicron variant exhibited lower levels of persistent virus in the lungs compared to the original SARS-CoV-2 strain.
Nicolas Huot, the first author of the study and a researcher in the Institut Pasteur’s HIV, Inflammation, and Persistence Unit, expressed astonishment at the discovery of viruses in immune cells known as alveolar macrophages long after regular PCR tests indicated no presence of the virus. Furthermore, these viruses were found capable of replication.
To better understand the role of innate immunity in controlling viral reservoirs, the scientists focused on natural killer (NK) cells. Muller-Trutwin emphasised the importance of studying the cellular response of innate immunity, stating, “Yet it has long been known that NK cells play an important role in controlling viral infections.”
The study revealed that in some cases, macrophages infected with SARS-CoV-2 became resistant to destruction by NK cells. However, in other instances, NK cells adapted to the infection, becoming adaptive NK cells and effectively destroying the resistant macrophages.
These findings shed light on the mechanism behind the presence of viral reservoirs and highlight the significance of adaptive NK cell production. Individuals with lower levels of long-term virus exhibited adaptive NK cell production, while those with higher levels not only lacked adaptive NK cells but also experienced reduced NK cell activity.