Vardy scored for England during the international break earlier this month but he is without a Premier League goal since a 4-1 defeat to Liverpool on September 10.
Simpson feels the Foxes' opponents are sitting deeper in a bid to nullify Vardy's threat but he is confident the forward will rediscover his scoring touch in the weeks ahead.
"Teams are playing a bit deeper, they are not letting us put the ball in behind for Jamie to chase because they know he is going to beat anyone in a race," said Simpson, as reported by ESPN.
"But with his pace and work rate he will score one and then go and score loads more.
"I know he is a striker and they love scoring goals but I have not seen a difference in him. In training he is putting them in from all over the place. He will score very soon."