COVID-19 is a contagious disease caused by the SARS-CoV-2 coronavirus. In January 2020, the disease spread worldwide, leading to the COVID-19 pandemic.
The symptoms of COVID-19 can vary but often include fever,[7] fatigue, cough, breathing difficulties, loss of smell, and loss of taste.[8][9][10] Symptoms may begin one to fourteen days after exposure to the virus. At least one-third of people who are infected do not develop noticeable symptoms.[11][12] Of those who develop symptoms noticeable enough to be classified as patients, most (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% develop critical symptoms (respiratory failure, shock, or multiorgan dysfunction).[13] Older people are at higher risk of developing severe symptoms. Some complications result in death. Some people continue to experience a range of effects (long COVID) for months or years after infection, and organ damage has been observed.[14] Multi-year studies on the long-term effects are ongoing.[15]
COVID-19 transmission occurs when infectious particles are inhaled or come into contact with the eyes, nose, or mouth. The risk is highest when people are in close proximity, but small airborne particles containing the virus can remain suspended in the air and travel over longer distances, particularly indoors. Transmission can also occur when people touch their eyes, nose, or mouth after touching surfaces or objects that have been contaminated by the virus. People remain contagious for up to 20 days and can spread the virus even if they do not develop symptoms.[16]
Testing methods for COVID-19 to detect the virus's nucleic acid include real-time reverse transcription polymerase chain reaction (RT-PCR),[17][18] transcription-mediated amplification,[17][18][19] and reverse transcription loop-mediated isothermal amplification (RT-LAMP)[17][18] from a nasopharyngeal swab.[20]
Several COVID-19 vaccines have been approved and distributed in various countries, many of which have launched mass vaccination campaigns. Other preventive measures include physical or social distancing, quarantining, ventilating indoor spaces, wearing face masks or coverings in public, covering coughs and sneezes, washing hands, and keeping unwashed hands away from the face. While drugs have been developed to inhibit the virus, the primary treatment remains symptomatic, managing the disease through supportive care, isolation, and experimental measures.