Quarantine accordingly delayed after source of infection (7)
I believe the answer is:
isolate
'quarantine' is the definition.
(I know that isolate is the is a more specific form of the action of quarantine.)
'accordingly delayed after source of infection' is the wordplay.
'accordingly' becomes 'so' (both can mean 'therefore', or 'as a result').
'delayed' becomes 'late' (running late).
'after' says to put letters next to each other.
'source of' suggests taking the first letters (the start - or source - of the word).
The first letter of 'infection' is 'i'.
'so'+'late'='solate'
'solate' after 'i' is 'ISOLATE'.
(Other definitions for isolate that I've seen before include "put away?" , "split up" , "Segregate or quarantine" , "Seclude" , "Point out" .)