I thought herd immunity required >90% of people to be resistant, but I guess that's only true for very contagious stuff like measles. According to https://en.wikipedia.org/wiki/Herd_immunity#Mechanics COVID-19 might only need 30% of the population to be resistant if it has an R0 of 1.4, or 75% if the R0 is 3.9. It's still a good chunk of the population but it's a lot different than I thought.