Don't we need to vaccinnate kids to reach herd immunity? Sure it doesn't make sense when you look at young people in isolation but that is beside the point.
The mRNA vaccines are sterile; there's no active virus or bacteria in them. It's also conclusively determined they reduce transmission.
(The sterility of a vaccine has no impact on its ability to reduce transmission, anyways; they're not linked. Live-virus vaccines like the flu nasal spray vaccine can still prevent disease.)
If we get to 60% of the total population plus 25% of the rest being immune from recovery, that is 70% total.