Where i come from, bullet proof vests are used to stop rounds aimed intentionally at one's center of mass; hopefully, the rating of the vest will exceed the strength of the round employed.
i believe in most departments these days, bullet proof vests are worn routinely when on patrol.
They don't always work. Just before I retired, I donated two weeks leave to the widow of a ranger who caught an AK-47 round that sneaked in between the seams of his vest.
I'm not an expert, but I'm pretty sure that the soft vests won't stop that round. Even the ceramic plates have gaps where the plates don't overlap, not to mention they can fail w/ repeated hits.