Rt really offers additional value to Ro. It's great to know that collective efforts such as mask wearing could keep the Rt down, easing a bit on the minimum vaccine coverage to achieve herd immunity threshold.

I also didn't know there's a difference between efficacy and effectiveness. Guess I have much more to learn. Indeed, vaccine trials have exclusion criteria, such as those with immunocompromised immune system and allergies (if I'm not mistaken). So, nobody is quite sure how vaccines would perform in such individuals.