> For instance if Delta has an R0 of 8, and we're 100% vaccinated, and the vaccine has an efficacy of 85% against infection, the resultant Rt would be 1.2:
For herd immunity, you also need to take into account that infected people—even symptomatic ones—are less infectious to others, if they're vaccinated.
Yeah, I'm familiar with that - I think that can be bundled into the efficacy number if you look at it as "efficacy against infecting others".
Last I heard, the CDC gave a 95% CI of the mRNA vaccines being 26% - 84% against infection (from Delta), and there's an additional 40% - 60% protection against infecting others (I've seen that estimate in multiple places but I don't know the source). If that's true, it suggests an overall range of 55.6 - 93.6 effectiveness against infecting others.
For herd immunity, you also need to take into account that infected people—even symptomatic ones—are less infectious to others, if they're vaccinated.