COVID-19 COVID-19 is a respiratory illness caused by the SARS-CoV-2 virus. For some people, COVID-19 feels like a mild cold. For others, it can cause more serious illness, especially in older adults, people who are pregnant, and people with certain medical conditions or weakened immune systems. Because COVID-19 symptoms can overlap with the common cold, flu, allergies, sinus infections, asthma flares, and pneumonia, it is important to know when home care is reasonable and whe