COVID-19: Global disease overview and health impacts

COVID-19 is a contagious illness 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 onset typically 1‑14 days after exposure. About 81% of diagnosed patients experience mild to moderate illness, 14% develop severe disease such as dyspnea or extensive lung involvement, and roughly 5% become critically ill with respiratory failure or multiorgan dysfunction. Older adults face higher risk of severe outcomes, and a portion of survivors experience prolonged effects known as long COVID.

Transmission occurs mainly through inhalation of infectious particles, close contact, and contaminated surfaces, with the virus remaining viable in the air and on objects for varying periods. People can be contagious for up to 20 days, even without symptoms. Diagnostic testing relies on nucleic‑acid detection methods such as RT‑PCR, transcription‑mediated amplification, and RT‑LAMP from nasopharyngeal swabs. Multiple vaccines have been authorized and are being distributed globally, complemented by preventive measures like physical distancing, mask use, ventilation, hand hygiene, and quarantine.