An infectious disease caused by the novel coronavirus SARS-CoV-2. COVID-19, or coronavirus disease 2019, was first identified in Wuhan, China, in late 2019. The disease manifests primarily as a lower respiratory illness, but it can affect multiple organ systems, including the cardiovascular, neurological, gastrointestinal, and renal systems. Symptoms include fever, cough, fatigue, shortness of breath, and loss of smell and taste. Some infected persons, especially children, are asymptomatic. Severe complications of COVID-19 include pneumonia, sepsis, acute respiratory distress syndrome, kidney failure, multiple organ dysfunction syndrome, and cytokine storm. Treatments currently involve symptom management and supportive care. Mortality varies by country and region, but approximately 6 percent of people living in the United States who are diagnosed with COVID-19 expire.[1] 1

A broad category of small proteins (~5-20 kDa) that are important in cell signaling. Cytokines are short-lived proteins that are released by cells to regulate the function of other cells. Sources of cytokines include macrophages, B lymphocytes, mast cells, endothelial cells, fibroblasts, and various stromal cells. Types of cytokines include chemokines, interferons, interleukins, lymphokines, and tumor necrosis factor.

A hyperinflammatory response to infection. Cytokine storm is characterized by the overproduction of immune cells and pro-inflammatory cytokines. A frequent complication of cytokine storm is multiple organ dysfunction. Cytokine storm is often present in severe cases of COVID-19.

A type of white blood cell. Macrophages engulf and digest cellular debris, foreign substances, microbes, cancer cells, and oxidized LDL in a process called phagocytosis. After phagocytizing oxidized LDL, macrophages are referred to as foam cells.

A type of white blood cell, also known as a granulocyte. Neutrophils are the most abundant form of blood cell, comprising approximately 60 percent of total cells. They ingest, kill, and digest microbial pathogens, and are the first cells recruited to acute sites of injury. Neutrophils can infiltrate brain structures, driving inflammation and increasing the risk for neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease.

In general, anything that can produce disease. Typically, the term is used to describe an infectious agent such as a virus, bacterium, prion, fungus, or other microorganism.

A study in which people are randomly allocated to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The control may be a standard practice, a placebo, or no intervention at all.

A fat-soluble vitamin stored in the liver and fatty tissues. Vitamin D plays key roles in several physiological processes, such as the regulation of blood pressure, calcium homeostasis, immune function, and the regulation of cell growth. In the skin, vitamin D decreases proliferation and enhances differentiation. Vitamin D synthesis begins when 7-dehydrocholesterol, which is found primarily in the skin’s epidermal layer, reacts to ultraviolet light and converts to vitamin D. Subsequent processes convert D to calcitriol, the active form of the vitamin. Vitamin D can be obtained from dietary sources, too, such as salmon, mushrooms, and many fortified foods.