COVID-19 is a type of coronavirus, which is a small germ (too small to see without a microscope) that can spread and cause illness in people. COVID-19 causes flu-like symptoms such as a dry cough, shortness of breath, fever, and body aches. COVID-19 mostly affects the respiratory system. While most infections are not dangerous, it can cause pneumonia (a serious infection of the lungs) and can be deadly in severe cases.