COVID-19 is an infectious disease caused by extreme acute coronavirus 2 respiratory syndrome (SARS-CoV-2). In December 2019, in Wuhan, China, the first case was found. Since then, the disease has spread internationally, resulting in an ongoing pandemic. A group of associated RNA viruses that cause diseases in mammals and birds are coronaviruses. They trigger respiratory tract infections in humans and birds that can range from mild to lethal. Some cases of common cold (which is often caused by other viruses, mainly rhinoviruses) include mild illnesses in humans, whereas more lethal variants can cause SARS, MERS, and COVID-19 among cows and pigs.