As for IL-4 in migraine group [3.52 (3.97) pg/mL], in encephalitis with headache group [2.99 (3.25) pg/mL], in pneumonia without headache group [2.44 (1.87) pg/mL], there were statistical differences in the overall distribution of IL-4 levels among the three groups (H = 12.81, p = 0.002). This evidence concerns the gene IL4 and viral encephalitis.