Leicester were awarded a penalty three minutes into first-half stoppage time when Serge Aurier barged into James Justin and brought him down. Vardy stepped up to take the spot kick and converted it down the middle.
It looked like Leicester had scored their second of the afternoon two minutes into the second-half when James Maddison slotted the ball home.
A VAR review, however, showed he was marginally offside and the goal was disallowed.
There was no such uncertainty 12 minutes later when Marc Albrighton crossed a ball into the box which Vardy got a head to. His shot careened off the knee of Alderweireld and into the back of his own net.