Analysis of "herd immunity" using the Sorites Paradox

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:


on the subject of ''free will'

While emailing back and forwards to a friend who's scientifically minded (and credentialed), we got into the nitty-gritty of the interpretations of quantum mechanics, and what it all means as far as 'free will' is concerned, and our daily lives.

My friend doesn't believe in any 'genuine' free-will, in that the choices we make are all, in a sense, 'determined' by forces or systems beyond ourselves (technically speaking, by downward causative influences).