It's all estimates, of course, but there's some good reading about what factors effect the herd immunity threshold here: https://en.wikipedia.org/wiki/Herd_immunity#Mechanics They estimate 50-83% vaccination threshold to achieve herd immunity for COVID-19. I believe the citation is this study, but I admit my ability to read scientific papers is lacking: https://pubmed.ncbi.nlm.nih.gov/32433946/