COVID-19 Overview: Symptoms, Transmission, Testing and Vaccines

COVID-19 is a contagious disease caused by the SARS‑CoV‑2 virus, responsible for a global pandemic that began in early 2020. Common symptoms include fever, fatigue, cough, breathing difficulties, loss of smell and taste, with onset typically 1‑14 days after exposure. Approximately 81% of symptomatic patients experience mild to moderate illness, 14% develop severe disease requiring oxygen support, and about 5% become critically ill with respiratory failure or multiorgan dysfunction. Older adults are at higher risk of severe outcomes, and a proportion of survivors experience prolonged effects known as long COVID.

Transmission occurs mainly through inhalation of infectious aerosols or droplets, especially in close-contact 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 detection methods such as RT‑PCR, transcription‑mediated amplification and RT‑LAMP from nasopharyngeal samples. Multiple vaccines have been approved and are being administered worldwide, alongside public‑health measures including physical distancing, mask use, ventilation, hand hygiene and quarantine to curb spread.