If I give the same vaccine to a group of people over age 65, then less than half of them will be protected by that first vaccination.
(I; give; the same vaccine; to a group of people over age 65) (less than half of them; will be protected; by that first vaccination; T:then)
I less than half of them
give will be protected
the same vaccine to a group of people over age 65
by that first vaccination T:then