Hospitals, schools, day care and public restrooms. These alone would significantly reduce the transmission of colds and flu. I suspect that making this mandatory for those locations alone would do more to minimize the spread of infectious diseases than mandatory vaccines.
Simply using Titanium Dioxide paints and UV lights might solve a whole bunch of problems...................or create a bunch more...................
When you kill of competing germs the “survivors” are often drug resistant “super bugs.” People typically get infected with them in hospitals.