What is herd immunity? And how do we get there on COVID-19?

Add to the pandemic lexicon another once-obscure term that’s come into common usage: “herd immunity.”

Along with “flatten the curve,” “social distancing” and “super spreader,” it’s a phrase that prior to COVID-19 was casually uttered mainly by epidemiologists and public health officials. But while the meanings of those other terms are now clear to many, herd immunity is a concept that is more complex, more nuanced and often misunderstood, scientists say.