COVID-19 is a contagious disease caused by the SARS‑CoV‑2 virus that spread worldwide after January 2020, leading to a global pandemic. Common symptoms include fever, fatigue, cough, breathing difficulty, loss of smell and taste, with incubation of one to fourteen days. About one‑third of infections are asymptomatic; of symptomatic cases, roughly 81% experience mild to moderate illness, 14% develop severe disease, and 5% become critical, with higher risk among older adults.
Transmission occurs primarily through inhalation of infectious particles, especially in close indoor settings, and can also happen via contaminated surfaces. People may remain contagious for up to 20 days, even without symptoms. Diagnostic testing relies on nucleic‑acid methods such as RT‑PCR, transcription‑mediated amplification, and RT‑LAMP from nasopharyngeal samples. Multiple vaccines have been authorized and are being administered globally, alongside preventive measures like physical distancing, mask use, ventilation, hand hygiene, and quarantine.
While many cases resolve with supportive care, severe infections can lead to respiratory failure, shock, or multiorgan dysfunction, and long‑COVID may cause lingering health issues for months or years. Ongoing studies continue to evaluate long‑term effects and treatment options.