Covid-19, herd immunity and common sense

There has been a LOT of talk in the media, various forums, twitter, etc, about "herd immunity" in regards to the corona virus pandemic.

The idea, basically, is that if enough people catch and subsequently become immune to the virus, the virus will "look around" for new hosts within the population, as some have suggested, and finding none available, recede and eventually die out.

That "looking around" suggests viruses are alive, seeking to reproduce like bacteria and fungi.

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: