Also wait a couple of weeks after he's totally cleared from being sick. Sometimes they take a little while to recover and body catching up even when they seem to be fine. If, after those 2 weeks he continues to wake early, we can design a plan for wake to sleep, but im thinking he'll be fine by then if you keep consistant with your schedule and an early bedtime to help him catch up on lost sleep.
HTH and that he gets back to his old self soon!