COVID 19 is caused by the SARS CoV 2 virus, which spreads mainly through respiratory droplets and aerosols released when an infected person breathes, talks, coughs or sneezes. Transmission is more likely in poorly ventilated indoor spaces and crowded settings. The virus can also contaminate surfaces, but this is a less important route compared with inhalation of infectious particles.

After infection, the virus primarily targets cells in the respiratory tract by binding to ACE2 receptors. The incubation period is typically 3 to 5 days. Symptoms range from none at all to severe pneumonia and multi organ failure. Common manifestations include fever, cough, fatigue, loss of smell and taste, and shortness of breath. Some patients develop blood clotting problems and a strong inflammatory response that can damage lungs and other organs. Older adults and people with chronic conditions such as heart disease, diabetes and obesity face higher risks of severe disease and death.

Diagnosis relies on detecting viral RNA with PCR tests and, in some cases, rapid antigen tests. Treatment for mild cases focuses on rest and symptom relief, while more severe illness can require oxygen, antiviral drugs, corticosteroids and intensive care support.

Vaccines using mRNA, viral vector and protein based technologies have been central for prevention. They train the immune system to recognize the spike protein of the virus and reduce the risk of severe disease, hospitalization and death. As the virus continues to evolve, new variants can partially evade immunity, making updated vaccines, good ventilation, high quality masks and timely testing important tools for ongoing control.