Analysis of herd immunity using the Sorites Paradox

[See supplemental article Covid-19, herd immunity and common sense]

When the subject of vaccination1 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"1
. From Wikipedia2 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: