[taxcontrol]

There is no such thing as herd immunity as no immuity is provided. What is call “herd immunity” is actually a simple lack of exposure. Once an infected person from outside the herd enters into the population, those that never developed immunity can be infected.

[Steve_Seattle]

"What is call “herd immunity” is actually a simple lack of exposure. Once an infected person from outside the herd enters into the population, those that never developed immunity can be infected."

That's not how I understand herd immunity; it's almost the opposite of my understanding. I thought herd immunity is achieved when a certain percentage of the population IS exposed, resulting in a couple of different things: there are no longer sufficient vulnerable "hosts" to spread the disease, so the disease begins to "starve" and die out; many people develop antibodies, short or long term; and the disease itself often weakens and mutates into less harmful forms.

[amihow]

What you describe can herd immunity if the population the unexposed walks into has built a high percentage of people who are immune. By full blown disease or by universal masking.