ΔE 31.3, loose: different enough that you should pick on purpose. Vampiric Purple is a little darker, much more muted, warmer than Deep Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Vampiric Purple is a little darker, much more muted, warmer than Deep Blue.
The same difference applies the other way round: Deep Blue is a little lighter, much more saturated, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Deep Blue on the colour wheel See Vampiric Purple on the colour wheel
All matches: Deep Blue equivalents · Vampiric Purple equivalents