Right, and that's where vaccine efficacy comes into play. If r0 is 6 and HIT is 83.3%, but efficacy is only 90%, then you actually need about 93% vaccinated. A

Right, and that's where vaccine efficacy comes into play. If r0 is 6 and HIT is 83.3%, but efficacy is only 90%, then you actually need about 93% vaccinated. And for herd immunity, what matters is transmission, and the vaccine efficacies for asymptomatic infection are pretty low; 50-60%. So mathematically impossible without severe lockdowns and/or improved vaccines that are better at preventing transmission.