Immune boost for my son

My son recently was diagnosed with mononucleosis, he is 7 and 1/2 years old and is a great eater and hardly ever sick. This virus really has made him fatigued and upset, however, he is on his way to recovery. I normally give him the VA essentials multivitamin for kids and Carlson DHA chewables for kids and since cold and flu season began daily dose of Culturelle. Since being diagnosed with Mononucleosis the conventional treatment is rest and fluids and treat the fever if present, however, I want his immune system to get stronger, in addition to his normal regimen mentioned above I added a product called: Sambucus for kids. This product contains: Elderberry, Echinacea, Propolis and also extra Vitamin D3. He is doing great, more energy and no fever and on his way to a full recovery hopefully.