When you say share a vibrator, I am not sure exactly what you mean.
Do you mean lending a vibrator, or are you referring to using it simultaneously
with a lover? The reason I ask is that my answer depends on what you are asking.
If you are wanting to let someone borrow a sex toy, simply washing it thoroughly
with soap and hot water will kill most things. If you want to be extra safe,
soaking it in bleach, then thoroughly rinsing it again with soap and water,
should be more than sufficient.
On the other hand, if you are wanting to use a sex toy such as a vibrator
simultaneously with a partner, you have to be more careful. The easiest way to
protect yourself and your partner is to put a condom on the vibrator. Then,
remove it and put on a new condom each time it changes hands.
Of course, it all depends on what kind of toy you are using and how you are
using it. What you want to avoid is exchanging any type of body fluids if you
have any concerns about sexually transmitted diseases. That the exchange occurs
via a sex toy is irrelevant. If you don't want to use condoms, plastic wrap can
work in a pinch, or if you don't mind taking a break to wash the toys
thoroughly, that works as well.