Coronavirus disease 19; Immunosuppressed; Liver transplant; Pneumocystis pneumonia; antibody production; antibody titer; CD4+ T lymphocyte; clinical trial (topic); coinfection; coronavirus disease 2019/dt [Drug Therapy]; coronavirus disease 2019/ep [Epidemiology]; coronavirus disease 2019/pc [Prevention]; COVID-19 serological testing; critically ill patient; cytomegalovirus infection; delayed diagnosis; disease severity; gold standard; graft rejection/co [Complication]; hospital admission; human; hypoxemia/di [Diagnosis]; hypoxemic respiratory failure/th [Therapy]; immune response; immunocompromised patient; immunoglobulin deficiency/co [Complication]; immunosuppressive treatment; incidence; intensive care unit; lactate dehydrogenase blood level; letter; liver transplantation; lung infiltrate/di [Diagnosis]; lung lavage; lymphocyte count; lymphocytopenia; morbidity; mortality; nasopharyngeal swab; pandemic; Pneumocystis jiroveci; Pneumocystis pneumonia/di [Diagnosis]; postoperative complication/co [Complication]; prophylaxis; publication; Severe acute respiratory syndrome coronavirus 2; thorax radiography; vaccine immunogenicity; veno-venous ECMO; beta glucan/ec [Endogenous Compound]; coronavirus spike glycoprotein/ec [Endogenous Compound]; immunoglobulin G antibody/ec [Endogenous Compound]; lactate dehydrogenase/ec [Endogenous Compound]; steroid; tozinameran/dt [Drug Therapy]