I'm also not convinced about the utility of rt either. At least not in real-time. Our local rt was around 0.78 in late September and now we have multiple times more infections than ever. And that was when most people were masking.
In any event, if a vaccine is 90% effective and you get the vaccine, it seems like the odds of you getting it and/or passing it on are extremely low. If the vast majority of high risk people and health-care workers are vaccinated in the first few months, then risk of serious illness or death would seem to be very very low.
Then again, I'm not an epidemiologist.