ACE2, Angiotensin converting enzime-2; APC, Antigen-presenting cell; BCG, Bacillus Calmette-Guérin; BV, Bacterial vaccine; Bacillus calmette-guérin; Bacterial vaccine; CCL-5, Chemokine (C­C motif) ligand 5; CI, Confidence interval; CNS, Central nervous system; COVID-19; COVID-19, Coronavirus disease-2019; CXCR3A, CXC chemokine receptor 3A; DAMPs, Damage-associated molecular patterns; DC, Dendritic cell; DLE, Dialyzable leukocyte extract; Exercise; Gαs: G protein coupled receptor alfa-subunits, HSP; Heat shock proteins, HLA-DR; Immune response; Immunoglobulin, IGFBP6; Innate; Insulin-like growth-factor-binding-protein 6, IL; Intercellular adhesion molecule type 1, IFN; Interferon, IG; Interleukin, MBSR; MCP-1, Monocyte chemoattractant protein-1; MMR; MODS, Multi-organ dysfunction syndrome; Major histocompatibility complex class II cell surface receptor, ICAM-1; Mindfulness; Mindfulness-based stress reduction, mCa++: Intramitochondrial calcium; MyD88, Myeloid differentiation primary response 88; NF-κB, Nuclear factor kappaB; NK, Natural killer; NK-Cell; NOD2, Nucleotide-binding oligomerization domain-containing protein 2; OR, Odds ratio; OxPhos: Oxidative phosphorylation, PAMPs; PKC, Protein kinase C; PPD, Purified protein derivative (tuberculin); PUFA, Polyunsaturated fatty acid; Pathogen-associated molecular patterns, PBMC; Peripheral blood mononuclear cell, PI3K/Akt: Phosphatidylinositol 3-kinase pathway; R0: Basic reproduction number, REM; Rapid eye movement, RIPK2; Reactive nitrogen species, ROS; Reactive oxygen species, SARS-CoV-2; Receptor iteracting serine/threonine kinase 2, RNA; Ribonucleic acid, RNS; Severe acute respiratory syndrome coronavirus 2, SIRS; Sleep; Systemic inflammatory response syndrome, TCR:T-cell receptor; TLR, Toll-like receptor; TNF-α, Tumor necrosis factor alpha; TRPV, Thermolabile calcium channels; Th, T helper-cell; Trained immunity; URTI, Upper-respiratory tract infection