Been there, done that. The smell is in the foam, underneath the leather. The acid in vomit seeps through stitching very fast. You might have wiped the leather but underneath will still smell.
You said rear seats, in our cars it has foam exposed on the bottom (leather is only wraps top and sides). You can try to dose that with odor killers once you remove them (very easy just pop them straight up, no screws or anything)
Best of luck