a vibrato is a pitch modulation
Doowop dooby doo doowop doowah doolang
Blue days black nights doowah doolang!
How much are you changing the pitch?

It shouldn't be a drastic change to the pitch, unless of course the song specifies it.
My Last.fm
USA Fender Stratocaster | Roland Cube 60 | VOX ToneLab LE
Yes, the pitch HAS to change for it be vibrato. How much the pitch changes is dependent on the musical passage. But everyone else has said this already.
"I am a remnant of the Forever Origin"

"The forest of October sleeps silent when I depart
The web of time hides my last trace
My blaze travel the last universe
Like the sights of magic
Wrapped in aeons
My mind is one with my soul"
vibrato is all about pitch change...
but it's that it should not go the other note....