A MILD case of COVID-19 causes mild fever, headache, body aches and cough. A SEVERE case of COVID-19 causes fever, cough and shortness of breath (i.e., difficulty breathing while doing daily activities, going up stairs, walking, eating, bathing, sleeping, talking, etc. and is NOT related to a previous health condition). Some patients may develop pneumonia. Symptoms appear two-14 days after exposure.