COVID-19 is an illness that infects the lungs. You may hear it called COVID or coronavirus disease 2019. It's caused by a type of coronavirus. The virus is called SARS-CoV-2. There are many types of coronaviruses. They are a common cause of colds and bronchitis. They can cause a lung infection called pneumonia. Symptoms can range from mild to severe. Some people have no symptoms. These types of viruses are also found in some animals.
Viruses change (mutate) all the time. The changes lead to different forms of a virus. These are called variants. COVID-19 variants may spread more easily from person to person. They may cause milder symptoms. Or they may cause more severe symptoms.
The virus spreads and infects people easily. It can infect a person more easily if they are not immune to it. The virus most often spreads through droplets of fluid that a person coughs or sneezes into the air. In some cases, you can get it from touching a surface with the virus on it and then touching your eyes, nose, or mouth.