Biography of Little Willie John at Billboard. He was all of 18 when "Fever" topped Billboard's R&B chart.
The Billboard biography claims that Peggy Lee copied Little Willie John's original "note for note".
Apparently, somebody is overly sensitive or just doesn't have much of an ear for music. A single listening makes it obvious that Peggy Lee reworked this song in her own inimitable style.
Which Elvis wasn't hesitant to copy, pretty much note for note. (His version appears on his Elvis is Back! LP and wasn't released as a single.)
The rock'n'roll version, which spent a few weeks in the top 10 in December 1965.
The Peggy Lee Bio-Discography And Videography:Observations About The Song "Fever".