COVID-19 disease overview: symptoms, transmission and vaccines

COVID-19 is a contagious illness caused by the SARS‑CoV‑2 virus that spread worldwide from January 2020, leading to a global pandemic. Common symptoms include fever, fatigue, cough, breathing difficulty, loss of smell and taste; about 81% of diagnosed patients experience mild to moderate illness, 14% develop severe disease, and roughly 5% become critical. Older adults face a higher risk of severe outcomes, and a portion of survivors experience long‑COVID effects lasting months or years.

The virus transmits mainly through inhaled respiratory particles, close contact, and contaminated surfaces, with contagiousness lasting up to 20 days. Diagnostic methods include RT‑PCR, transcription‑mediated amplification and RT‑LAMP from nasopharyngeal swabs. Multiple vaccines have received approval and are being administered globally, while public‑health measures such as physical distancing, mask‑wearing, ventilation, quarantine and hand hygiene remain essential to limit spread.