The purpose of this research is to: To show whether the study drug RLF-100 along with standard of care is better than standard of care alone in preventing progression from Severe COVID-19 to Critical-COVID-19 with respiratory failure, to determine whether RLF-100 along with standard of care improves the ability of the lungs to transmit oxygen to your blood, to determine whether RLF-100 along with standard of care shortens the number of days in hospital; reduces the need for additional oxygen, shortness of breath (dyspnea) and/or the need to be transferred to the ICU, or otherwise improves the course of Severe COVID-19.