The comparable diagnostic potential of anti-measles dIgA (area under the curve, AUC: 0.920–0.945) to anti-measles IgM (AUC: 0.986–0.995) suggests that dIgA may be a new blood-based marker of acute measles, independent of IgM, which merits further investigation and optimization. Here, CD40LG is linked to measles.