First patient model since axed (5,4)

I believe the answer is:

index case

'first patient' is the definition.
(first identified case of a disease)

'model since axed' is the wordplay.
'model' indicates an anagram (letters must be modelled into a new form ).
'since'+'axed'='sinceaxed'
'sinceaxed' is an anagram of 'INDEX CASE'.

I've seen this clue in The Times.

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