In MGS 4, how exactly do you beat vamp?

Question

I can't get past this level.

Answer 1

Shoot till you knock him out, un-select your weapons and get the syringe from your inventory, get behind him, when he's getting up use CQC to grab a hold of him, use the syringe on him while holding him. Ta-dah..you beat vamp.

The syringe suppresses nanomachine activity and thus greatly reduces his ability to recover. Don't worry, once you inject him Raiden will take care of the rest while you keep the Gekkos busy...preferably with your Rail Gun.

Answer 2

You stick 'im with the syringe with the triangle button.