Several months after infection with SARS-CoV-2, some patients still have symptoms: a phenomenon commonly referred to as “long COVID”. In new research, teams from Inserm and Université Paris Cité[1], in collaboration with the University of Minho in Braga (Portugal), have shown that this could be explained biologically by abnormalities of the immune system associated with the persistence of the virus in the mucous membranes. These findings, published in Nature Communication, could in the longer term pave the way for a diagnostic tool for long COVID.
Despite the fact that various studies consider long COVID to affect between 10 and 30% of people infected with SARS-CoV-2, its diagnosis and treatment remain difficult. The team of Inserm researcher Jérôme Estaquier, in collaboration with that of Ricardo Silvestre at University of Minho in Portugal, is conducting research to explain this phenomenon from the biological point of view.
At the present time, few biological criteria, apart from the persistence of symptoms beyond three months after the acute infection, enable its diagnosis. Once a patient is not fully recovered after this period, they are considered to have long COVID. Without a more reliable means of diagnosis, it is difficult to offer the appropriate care.
In order to better understand long COVID and find diagnostic markers, the researchers studied the immune systems of 164 people six months after they were infected. They analysed the blood samples of 127 people, half of whom with long COVID (fatigue, shortness of breath, cough, muscle or chest pain, anxiety, etc.) and those of 37 controls who had not been infected.
The researchers focused on certain immune cells, namely the T cells (including CD8 cells) involved in eliminating the virus, and the SARS-CoV-2 antibodies. In addition, they had blood samples that were taken during the acute phase of the disease for 72 of these patients, enabling them to retrospectively compare the level of inflammation at the early stage in those who went on to develop long COVID or not.