While the top priority is to protect the vulnerable directly, I believe the idea behind minimizing social contact is to stop the spread generally so that when vulnerable people do come into contact with others, which is almost inevitable, those others are themselves less likely to be carrying the virus, possibly unknowingly as the symptoms do not manifest immediately. And to buy time to strengthen the health services to cope with the spike in sick people. The Italians have had a much more stringent lockdown than we have, for longer, and their cases are still rising quite sharply.