Winter illness (3)
I believe the answer is:
flu
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">winter 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 "Common infection" , "A bad winter bug" , "Infection reduced" , "Highly contagious viral disease" , "Winter ailment" .)