Interesting idea, but if everyone between the ages of 17 and 35 goes out and gets sick it doesn't matter how isolated your 90 year old grandma tries to be, she's probably going to get sick too.

The point of having society, and of having governments, is that cooperation allows us all to lead longer, healthier, more fulfilling lives. You can't just discard the necessity of cooperation in specific instances where the benefit you personally receive is lower than the amount of effort you need to put in.