It’s hard to get, too.
I suspect that fewer than 1/10 people can tell you what HERD immunity is, though virtually everyone has HEARD about it.
And, probably fewer than 1/100 can tell you how it works.
No wonder it is so hard to achieve! Perhaps we should start out by using language that people can understand and remember.
Viruses are nasty little buggers that get into humans by various means. They exist only to grow, which means finding more human hosts.
It also happens that when humans get infected and after most of them recover, they cannot get infected again – at least for a while – and thus cannot retransmit the virus to others.
Statisticians discovered 100 years ago that when a high enough share of a population had become immune, whether by previous infection or vaccination, the buggers run out of new homes and begin to die out from the lack of hosts.
They coined the phrase “HERD immunity” to describe this phenomenon because when a large enough share of the herd (of animals) had become immune the ‘game’ was over.
This really has nothing to do with ears.
It does, however, have everything to do with tongues. And one formerly-presidential tongue, in particular, needs to get frozen to a lamppost at the South Pole so that it can no longer be HEARD.