Herd immunity

[Len Moaven]

G'day folks

Just a little bee in my bonnet. I may be wrong but my understanding was 
that herd immunity related to the protection of susceptibles in a 
population of protected individuals. However I have now seen a number of 
references to herd immunity (in this newsgroup and Dec Nature Medicine 
re Salk versus Sabin polio vaccine) which intimates that the protection 
conferred by acquisition of the live vaacine from deliberately immunised 
individuals to unimmunised individuals constitutes "herd immunity".

Isn't this an incorrect use of the term? I did not think herd immunity 
related to protected individuals no matter how they acquired there 
infection. 

Like-minded postings and support is welcomed although a cogent argument 
may sway me.

Len