Spit and phlegm contain germs, at a more concentrated level, that are expelled from body when coughing and sneezing.
The droplets reach passers by, spreading Corona viruses, Flu and Epstein Barr to name but a few.
As well as sneezing/coughing into tissue, regular hand washing - it would be good practice to ban spitting, or to at least promote good hygiene practice such as spitting into tissue and putting it in the bin to prevent spread of germs.