@Walter Hinteler,
Well couldn't someone immune themselves be spreading it to others via touching and contaminating other items that people touch? Droplets can be on their skin, clothes anything they have touched, and spread to others.
Others can deposit the virus in an immune persons mucus membranes, and then be spread by their cough or sneeze.
I mean, it's not like BAM, the virus somehow gets in or on an immune person, and it instantly dies. They can carry it from point A to point B and spread it. Can't they?