Some sobering math on what it takes to reach herd immunity with B.1.1.7, given that vaccines and infection aren't perfect preventers of future infection or transmission.
With an R0 of 4.3, they're looking to have razor-thin levels of herd immunity with 95% of over 55s vaccinated and 85% of under 55s. They should reach that level around the end of June.
Finding ways to boost uptake to 95%, and/or to vaccinate children, would give some margin for error. That's important, because new variants are coming and herd immunity isn't uniform across the country.
If those numbers are close to accurate, the US is on track to miss herd immunity by a fairly wide margin if current hesitancy levels hold. An R0 of 4.3 is much, much tougher than a 2.7.