Depends on the body armor used (soft, hard, thick, thin, etc.). Also, most armor plates cover vital regions (e.g., heart, chest,), and not the entire body. Also depends on the decision of the officer to wear/not wear armor that day.
Most departments issue IIIA vests. Will stop all pistol calibers. NIJ level III (stand alone rifle) vary in weight from 2.9 lbs (DKX) to 8-10 lbs for AR500 steel. Those weights are per plate, so X2 for front and rear coverage.
Knowing that rifle fire is inbound, wearing IIIa gear, and still running toward the gunfire....
Brave, honorable folk!
KYPD