Not proven effective. Many "non-medical" supplements, foods, herbs, and techniques are claimed to "boost" the immune system, but none have been proven effective. The immune system is complex, and "boosting" it to make it act stronger is not always a good thing. In conditions like arthritis, thyroid disease, diabetes type 1, lupus, eczema, etc..., the immune system is over-acting and damaging the patient's own organs.
No magic pill. Many people are looking for some "magic pill" to "boost their immune system". There is no such pill. However, there is a way to boost your immune system, live a healthy lifestyle. Proper diet, proper sleep- wake cycles, healthy environment, proper exercise are the foundation of good health and good immune health. Supplements should be used selectively to supplement a healthy diet.
Nutrtion, herbs, etc. A good multivitamin & healthy diet helps. Many vitamins & minerals like vit a & d & zinc boost immunity. Avoid sweets and fried food. Many herbs like astragalus & ashwagandha help, as do medicinal mushrooms like reishi & shiitake. Reducing stress & getting adequate rest is crucial. Homeopathy & acupuncture help.The road to immunity by kenneth bock md is a wonderful book on how to boost immunity.