A Randomized, Double-Blind, Single Center, Efficacy and Safety Study of Allogeneic HB-adMSCs Against COVID-19.

Inclusion Criteria: * Men, and women 18 years of age or older * Participant works in a capacity that is characterized as high-risk or very high-risk * High-Risk Exposure jobs are those with high potential for exposure to known or suspected sources of COVID-19. * First responders, health care delivery and support staff (e.g., law enforcement, fire fighters, paramedics, doctors, nurses, and other hospital staff who must enter patients' rooms) exposed to individuals potentially having COVID-19. * Mortuary workers involved in preparing (e.g., for burial or cremation) the bodies of people who are known to have, or suspected of having, COVID-19 at the time of their death * Very High-Risk Exposure jobs are those with high potential for exposure to known or suspected sources of COVID-19 during specific medical, postmortem or laboratory procedures. * Health care workers (e.g., doctors, nurses, dentists, paramedics, emergency medical technicians) performing aerosol-generating procedures (e.g., intubation, cough induction procedures, bronchoscopies, some dental procedures and exams or invasive specimen collection) on known or suspected COVID-19 patients. * Health care or laboratory personnel collecting or handling specimens from known or suspected COVID-19 patients (e.g., manipulating cultures from known or suspected COVID-19 patients). * Morgue workers performing autopsies, which generally involve aerosol-generating procedures, on the bodies of people who are known to have, or suspected of having, COVID-19 at the time of their death * No signs or symptoms of infection, including but not limited to, body temperature \>100 F and pulse rate \> 100 BPM. * Subject provides written informed consent prior to initiation of any study procedures.--Agrees to the collection of venous blood per protocol. * Agrees to conformational testing for SARS-CoV-2 before end of study. Exclusion Criteria: * Women who are pregnant or lactating, or those who are not pregnant but do not take effective contraceptive measures * Patients who are participating in other clinical trials or have intake of investigational drug within the previous 30 days; * Inability to provide informed consent or to comply with test requirements; * Any medical disease or condition that, in the opinion of the site PI or sub-investigator, precludes study participation. Including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. * Patients who have received a stem cell treatment within one year. * Receipt of any other SARS-CoV-2 or other experimental coronavirus vaccine at any time prior to or during the study.