COVID-19 (Coronavirus disease 2019) is a contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first case was identified in Wuhan, China, in December 2019. It has since spread worldwide, leading to an ongoing pandemic.
Symptoms, which begin one to fourteen days after exposure to the virus vary, but often include fever, cough, fatigue, breathing difficulties, and loss of smell and taste. Most people (81%) develop mild to moderate symptoms (up to mild pneumonia), while 14% develop severe symptoms (dyspnea, hypoxia, or more than 50% lung involvement on imaging) and 5% of patients suffer critical symptoms (respiratory failure, shock, or multiorgan dysfunction). At least a third of the people who are infected remain asymptomatic and do not develop noticeable symptoms at any point in time but can spread the disease. Some patients continue to experience a range of effects—known as long COVID—for months after recovery and damage to organs has been observed.
The virus spreads mainly when an infected person is in close contact with another person. Small droplets and aerosols containing the virus can spread from an infected person's nose and mouth as they breathe, cough, sneeze, sing, or speak. Other people are infected if the virus gets into their mouth, nose or eyes. A person who is infected can transmit the virus to others up to two days before they themselves show symptoms, as can an individual who does not experience symptoms. People remain infectious for up to ten days in moderate cases, and two weeks in severe cases. The standard diagnosis method is by real-time reverse transcription polymerase chain reaction (rRT-PCR) from a nasopharyngeal swab.
Preventive measures include physical or social distancing, quarantining, ventilation of indoor spaces, covering coughs and sneezes, hand washing, and keeping unwashed hands away from the face. The use of face masks or coverings has been recommended in public settings to minimize the risk of transmissions. Several vaccines have been developed and various countries have initiated mass vaccination campaigns, but new strains continue to show up. (Information from Wikipedia)