Herd Immunity Doesn't Mean What Trump Thinks It Does 1

Thanks in no small part to the bloviating from politicians ranging from Boris Johnson to Donald Trump, talk of herd immunity has been inescapable during the coronavirus pandemic.

Herd immunity is the theory that once a certain percentage of the population is immune to an infection, the infection can no longer find new people to claim and will effectively disappear. We also call that “exhaustion of susceptibles,” meaning that once there are no more susceptible people, the infection dies out. That’s the common way communicable diseases are controlled either naturally, or through vaccination.

President Trump has flogged the concept as part of his broader suggestion that the pandemic will resolve itself. “It’s going to disappear—I still say it,” he said this week. “You’ll develop herd—like a herd mentality.” (It’s clear what he was trying to say.)