Influenza & Other Febrile Illnesses (as cause of H/A)

Anything that causes a fever can cause a headache.  If headache is prominent, & the absolutely only other symptom [no cough, myalgias, sore throat, nothing], consider serious CNS pathology.  But unless the patient looks ill, temporize with antipyretics until the fever’s been present >3 days.  Otherwise you’d be imaging or tapping everyone.