Immune dysregulation through longitudinal lymphocyte trajectories and their clinical determinants in hospitalised COVID-19 patients

Authors: José Pedro Cidade, Fabio Silvio Taccone, Luis Felipe Reyes, Laura Merson, Benjamin Lefevre, Barbara Wanjiru Citarella, Arie Zainul Fatoni, Pedro Póvoa and the ISARIC Characterization Group.

A large multinational analysis from the ISARIC cohort has shown that lymphopenia is not only common in hospitalised COVID-19 patients but also strongly associated with disease severity and mortality. Among more than 231,000 adults included in the study, over half were lymphopenic. Patients with low lymphocyte counts had significantly higher rates of ICU admission, organ support, and in-hospital death.

The study moved beyond single laboratory measurements and examined lymphocyte trends over time. Persistent lymphopenia—rather than transient reductions—was linked to a higher daily transition rate to death and poorer 28-day survival. Lower absolute lymphocyte counts were independently associated with increased mortality risk, even after adjustment for confounding variables.

Corticosteroid exposure was associated with a greater likelihood of entering and remaining in a lymphopenic state, and distinct recovery patterns were observed between survivors and non-survivors. These findings underscore the clinical value of serial lymphocyte monitoring and support a more dynamic approach to immune assessment in severe viral infections and sepsis, with potential implications for tailoring immunomodulatory therapies.