The Tricky Math of COVID-19 Herd Immunity | Quanta Magazine

The Tricky Math of COVID-19 Herd Immunity | Quanta Magazine

The thorny problem of herd immunity The concept of ‘herd immunity’ is fairly simple. When enough people are immune to COVID-19 — whether by vaccination or by having survived infection — the spread starts to slow because there are not enough people to infect. But how many need to be immune before that happens? It’s a tricky question, especially when the protection is acquired naturally, rather than by immunization. People are physically different in their susceptibility to infection. And where you live, and your living conditions, make a difference, too. The threshold could be much higher in densely packed cities — and the hardest-hit places in the world might already be close to reaching it.Quanta | 8 min read