Immune system supplements are scam, right?

Yes. If you mean otc supplements, herbs and the like claiming to "boost immunity", then yes they are unlikely to be effective.
Maybe. 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.