Studies show that COVID-19 causes long-term changes in the immune system

In a study recently published in the renowned journal Allergy, the MedUni Vienna research team shows that COVID-19 leads to significant long-term changes in the immune system, even in subtle cases. These findings may assist us better understand the long-term consequences of SARS-CoV-2 infection.

In the study, the team led by first authors Bernhard Kratzer and Pia Gattinger and principal investigators Rudolf Valenta and Winfried Pickl (all from the MedUni Center for Pathophysiology, Infection and Immunology in Vienna) examined vital immunological parameters in 133 people who had recovered from COVID-19 and 98 people who had not been infected. The number and composition of various immune cells, as well as cytokines and growth factors in the blood, which play a decisive role in regulating cell growth, were analyzed in recovered patients ten weeks and ten months after their initial infection. Since no COVID-19 vaccines were available during the follow-up period in 2020, all participants remained unvaccinated. This allowed the study authors to investigate the long-term effects of SARS-CoV-2 infection without the influence of vaccines.

A significant reduction in the number of immune cells in the blood

This was not entirely unexpected, as ten weeks after infection, convalescent patients showed clear signs of immune activation of both T and B cells, in contrast to the well individuals in the study.

Winfried Pickl

In addition, cytokines and growth factors in the blood were typical of remnants of an acute inflammatory process. A comparison with patient samples taken ten months after COVID-19 revealed an unexpected picture for the researchers: “Even after a subtle course of the disease, we found a significant reduction in immune cells in the blood,” says Winfried Pickl, providing details from the study. In addition, a well-known decrease in SARS-CoV-2-specific antibodies and a striking change in the patterns of growth factors in the blood were observed. For people recovering from COVID-19, this means that their immune system may no longer respond optimally to novel challenges. This could explain some of the observed sequelae of COVID-19, such as long COVID.

According to the researchers, the long-term consequences of COVID-19 are likely due to the infection and the resulting long-term impairment of the bone marrow, the central site of immune cell production. “Our results provide a possible explanation that some long-term consequences of COVID-19 may be related to SARS-CoV-2-induced damage to the cellular immune system and an apparent reduced maturation and/or emigration of immune cells from the bone marrow,” Winfried Pickl and Rudolf Valenta summarize the study. This hypothesis provides the basis for further studies to better understand the mechanisms underlying long COVID.