"All of the participants were employees of Cleveland Clinic."  
It seems unlikely that the employees of one of the best health clinics in the world reflect the behaviors of the general public.  Also, the US was still largely in a period of reduced social interaction (aka 'lock down').  There was no ability to track exposures.  Also, unlike Europe and Africa, the US (especially Ohio) had a minimal incidence of the other strains of this virus.  

All this adds up to a very weak study if one wants to assess the risk in the general society under normal conditions.