Herd immunity is vulnerable to the free rider problem. Individuals who lack immunity, including those who choose not to vaccinate, free ride off the herd immunity created by those who are immune. As the number of free riders in a population increases, outbreaks of preventable diseases become more common and more severe due to loss of herd immunity.

The freaking science teacher at my old school didn’t understand what herd immunity is. This was before COVID when vaccine retardedness was just a growing chorus of idiocy from right wing radio. Which the science teacher listened to constantly.