The article about “herd immunity” is oversimplifying about herd immunity being “when things start to slow down.” Even 20% immunity will likely slow down an epidemic … herd immunity is when growth is linear (vs exponential), ASSUMING NO OTHER MEASURES. The point is that, as more people gain immunity, the measures required to keep an epidemic in check gradually decrease.
“Herd immunity” needing a majority of the population also makes other assumptions, like that everyone is equally susceptible. Perhaps 50% of people can’t catch COVID due to some genetic difference or due to cross-immunity with other coronaviridae. This would explain the low household secondary attack rate — only about 15-25% of people sharing a home with a COVID case contract it themselves.
