COVID-19 infections can be mild to severe but factors that influence severity are poorly understood. Immune cells may become distressed, “exhausted” and ineffective at clearing infection. This is one likely reason that certain patients cannot fight COVID-19 infection efficiently and succumb to the disease. In this project, I will assess the role of immune cell exhaustion in determining the severity of infection, and the recovery from COVID, by using blood samples from a small cohort of patients with a range of disease severity managed at Galway University Hospital throughout the pandemic. I will optimize the use of human peripheral blood mononuclear cells to identify and characterize T-cell subpopulations with exhaustion phenotypes by developing panels of fluorochrome-labeled antibodies for spectral flow cytometry analysis. I will then correlate levels of T-cell markers with clinical parameters including inflammatory markers, length of stay, organ involvement. By the conclusion, I will have a clear picture of 1) the effect COVID-19 on immune cell exhaustion and 2) the correlation between levels of T-cell markers with different clinical parameters.