COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which spread globally starting in late 2019. The virus transmits primarily between people in close contact, often through tiny air droplets generated by breathing, talking, singing, coughing, or sneezing. Symptoms typically appear 2 to 14 days after exposure and can range from mild cold-like symptoms, such as congestion and sore throat, to no symptoms at all. Individuals who test positive without symptoms are considered asymptomatic, while those who develop symptoms later are presymptomatic; both groups can still transmit the virus to others.
Most people experience mild to moderate recovery, but older adults, specifically those aged 65 and older, and infants under six months face the highest risk of requiring hospital care. Serious illness risks are also elevated for individuals with weakened immune systems, such as those with cancer, HIV, or those taking immunosuppressive medications, as well as pregnant individuals. Other risk factors include existing medical conditions and living in group homes or lacking access to medical care. In rare cases, patients may develop multisystem inflammatory syndrome, known as MIS-C in children and MIS-A in adults, which involves inflammation of organs and tissues.
While most people recover without long-term effects, some report symptoms persisting for months, a condition often referred to as long COVID. Research continues into the specific long-term effects of the virus, which has been studied only since 2019. Vaccination may help prevent this post-COVID-19 syndrome. Other preventive measures recommended to limit spread include good indoor airflow, physical distancing, mask-wearing in appropriate settings, and good hygiene. It is noted that transmission from infected surfaces or pets is rare, though cats, dogs, hamsters, and ferrets have been documented to contract the virus.
Healthcare providers may prescribe medicine to block the spread of the virus in individuals at high risk of severe illness or plan regular health checks. Emergency care is advised for specific severe symptoms in adults and children. The current vaccination strategy aims to update protection against evolving variants, with the 2026-2027 formulas representing the latest regulatory approvals for use in the United States.
