That diseases come in waves seems like evidence of herd immunity to me. Like starting with a naive population you get a wave of infection. People become immune,

That diseases come in waves seems like evidence of herd immunity to me. Like starting with a naive population you get a wave of infection. People become immune, spreading (mostly) stops. Over the years immunity is weakened because of old people dying and new people being born. Eventually the fraction of the population that is immune is low enough that a new wave gets going.