"The kissing disease," for short

MONO

Fatigue and a sore throat often follow this common viral infection spread through saliva.

"The kissing disease" is a nickname for mononucleosis because it spreads easily through saliva, like when people kiss. The clue adds "for short," hinting at the common abbreviation "mono" instead of the full word. It’s a straightforward definition with a casual reference to how the illness is often talked about.