When the subject of vaccination is discussed within a group (e.g. online forum), and there are some within that group who are pro-vaccination, almost invariably they will at some point raise the issue of herd immunity.
First let's clarify what is meant by "herd immunity"
. From Wikipedia this:
"Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune"
There are, it seems to me, a number of aspects to this subject that need clarification: