Tons running activity to track virus contacts (7)
I believe the answer is:
tracing
'activity to track virus contacts' is the definition.
(as in contact tracing)
'tons running' is the wordplay.
'tons' becomes 't'.
'running' becomes 'racing' ('race' can be a synonym of 'run').
't'+'racing'='TRACING'
(Other definitions for tracing that I've seen before include "Finding by investigation" , "design" , "Tracking or outlining on transparent paper" , "Hunting down" , "produce copy?" .)