Ongoing mutation of viral infection a bad sign? (4)
I believe the answer is:
flux
'ongoing mutation' is the definition.
(flux means mutation or change)
'viral infection a bad sign?' is the wordplay.
'viral infection' becomes 'flu' (I've seen this before).
'a bad sign?' becomes 'X' (a cross can signify something wrong).
'flu'+'x'='FLUX'
'of' acts as a link.
(Other definitions for flux that I've seen before include "State of constant change" , "Flow of matter" , "constant changing" , "Continuous state of change" , "State of continual change" .)