Viral illness (3)
I believe the answer is:
flu
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">viral illness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for flu that I've seen before include "In brief, winter illness" , "Viral illness" , "Minor ailment" , "Mild infection" , "Viral infection (colloq.)" .)