He had linked up with the squad on Friday night after spending time in hospital this week for treatment on an infected finger.
The all-clear for Moody is a huge boost to England boss Andy Robinson as the world champions target a first victory in the tournament following defeats against Wales and France.
Moody's experience will be crucial in the heat of battle on Sunday, as he links up with back-row colleagues Joe Worsley and Martin Corry.
Had Moody failed to make it, then Robinson would have drafted in Gloucester's Andy Hazell and put Chris Jones on the bench.
But Robinson is now able to retain the starting line up he announced on Tuesday, which means Moody featuring and Hazel remaining among the replacements.