Quick Answer: Coronavirus disease 2019 is a contagious disease caused by the coronavirus SARS-CoV-2. Starting in January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic. In March 2020, the World Health Organization declared COVID-19 a global health emergency; they declared the end of the emergency in May 2023. The symptoms of COVID‑19 can vary but often include fever, fatigue, cough, breathing difficulties, loss of smell, and loss of taste. Symptoms may begin one to 14 days after exposure to the virus. At least a third of people who are infected do not develop noticeable symptoms. Of those who develop symptoms noticeable enough to be classified as patients, most develop mild to moderate symptoms, while 14% develop severe symptoms, and 5% develop critical symptoms. Older people have a higher risk of developing severe symptoms and dying. Some people experience persistent symptoms, for months or years after infection, including fatigue, cognitive issues and shortness of breath.