what u do well what i did use the syring naomi gave u.the i would equip a shotgun or
railgun. when he ghot close i would shoot him in the head. to knock him down. then grab
him then it will come up to press triangle do that and u get to the next scene. i would
agree that the next scene is a very good part.

if u want to kill vamp i suggest that u get better weapons like m4 custom just keep
shooting at him when the health bar of vamp is really really low like one more shot or
whatever make him get a little closer then equip syringe then as your weapon is none when
he tries to get up press and hold R1 after u got him u press triangle while holding the R1

To kill vamp, equip the syringe, the shoot him until his health bar is zero (recommend
railgun or machine gun e.g M4 Custom), then as he gets up CQC grab him and inject him with
the syringe.