Covid-19 Mutations Make Immunity Math Incredibly Daunting
New virus variants will make it harder to reach herd immunity, but vaccines should prevent them from killing us.
Mutations aren’t reason to despair
Photographer: Bloomberg
Since early in the Covid-19 pandemic, would-be prophets (most of them not infectious-disease epidemiologists) have been predicting that it would soon burn itself out as people recovered from the disease and developed immunity. So far they have been proved wrong again and again as temporary declines in new infections gave way to second and third waves.
Still, even infectious-disease epidemiologists agree that there is a point at which widespread immunity to a disease can cause it to decline or even disappear. This “herd immunity” threshold is calculated in its simplest form as a function of a disease’s basic reproduction number, R0, which is how many additional people each person with the disease can be expected to infect (in a population with no previous immunity that makes no behavioral changes in response to the disease). In this equation, the share of the population that needs to be immune to achieve herd immunity is 1 - 1/R0.