It is bad science to say covid-19 infections will create herd immunity: According to the signatories of an open letter called the Great Barrington Declaration, lockdown measures are doing more harm than good and we should open up society and let the virus rip. (...)
The mainstream media lapped up the disagreement narrative, but completely missed the fundamental problem with the declaration: its extremely dubious claims about herd immunity. This is central to the strategy, but the document badly fluffs the science.
Herd immunity is conceptually simple. If enough people become immune to an infectious agent, the entire herd is protected because infectious people rarely encounter a non-immune person, and so transmission fizzles out.
The level of individual immunity required to attain herd immunity depends on how infectious the virus is, as measured by R, the average number of people that each infectious person infects. The classic example is measles, which has an R number of around 15 and a herd immunity threshold of 95 per cent. The numbers for the coronavirus SARS-CoV-2 are about 3.5 and 60 to 70 per cent.
Herd immunity has only ever been attained by vaccination. But the declaration advocates naturally acquired immunity. In other words, letting between two-thirds and three-quarters of the population catch the virus.
