There are many ways that you can give your immune system a bit of a boost. Saying someone has low immunity means their defense system is weak, and when that happens, viruses and bacteria can harm your immune system. If you are always catching colds and flu, always feeling tired or have other issues related to low immunity, it’s time to strengthen your body. Vitamins A, C, E, and folic acid, and also zinc and selenium. That’s why a healthy diet is good for a strong immune system.