… sorry, no magic pill, no quick fix or no immediate boost. 
What works is,  good food, eaten regularly. This gives you good overall health, stronger internal body and better resistance to attack.      The immune ‘system’ is the body’s protection against nasty foreign bodies which can harm us.  But it is not only one ‘system’, as if it was an organ or a shield like our skin. The skin, an organ, is actually one part of the entire body’s immunity. If fact every cell in our body is part of the overall immunity.

    Improving our overall health is the most important thing.
To take good care of our bodies, we need to eat good food – wholefoods and a variety of foods. So much of our body’s proper functioning comes from the food we eat. What we eat affects our gut bacteria and good gut bacteria is a major player in the body’s immunity. Our body’s immunity is stronger when our cells are healthier.     … it is that simple.
Boosting Immunity … what really works  We all want to feel better.      Feeling better often means eating better, and it means work. When we say we want to ‘ boost our immunity’ … what we really mean is, we want a quick method of getting healthier.

      But there is one problems here – cells ( our immune system) do not get healthier with a boost of anything. They are healthy because of an overall, continuous, long term proper intake of healthy food.         To boost our immunity we need to think long term.
If we are feeling low, overly tired, run down, then we must look at our lifestyle and what we eat. Then bit by bit, if we choose to eat good food, we will start to feel better and better.   Takes time, a bit of effort, but it works.
Eating Less  …
A little fasting can do a lot of good…      It may seem strange that to get better we are doing less, holding back rather than actively doing something, but that is the best way. The body, as part of its make-up has natural mechanisms to heal itself. Often outside interference actually slows down the healing. Let the body do its work.        And to eat for a short period of time allows the body to rest. The stomach, digestion process, takes so much energy from the body that it gets tired after each meal, especially after big, heavy meals.         When you allow the stomach to rest, blood and energy required for digestion get directed to other parts of the body to repair and to cleanse.
Sit back and let the healing begin.  

Do Nothing …rest ….for a short while.           Exercise, fitness is very good for you. To have the body moving means the blood is being well circulated. The blood is the main carrier of food and healing to the cells, so the better the circulation, the better we feel.        Moving about is all that is needed, regularly. Of course exercise also has an effect on our mental well being, which affects our immunity … after all, everything is connected in our bodies.        But there is a time when we should do nothing, rest. Rest the body, give it a chance to recuperate.  Sleep is the best rest and the best form of healing. When we lack sleep we often get sick because lack of sleep weakens the body and our immunity.      Whenever I feel unwell, I know that sleep is needed, before any kind of medication. A few good nights sleep can heal so much.      So sometimes when you are feeling low, stop.
Give the body a rest and if possible sleep, get a good night sleep. One always feels better in the morning.

But Can I Do Anything Now ?  … yes, boost your energy.

When you feel run down, you can rest, you can fast. But if you choose not to do these things and really want to eat, because you are hungry, then eat food that will give you energy. Foods that give you energy are whole foods – unrefined foods; brown rice, any whole grain, beans and vegetable. And eat small meals, you will not feel tired afterwards.      After being sick, and just about better, that time when you have not eaten but now are hungry, I find the best thing is a good soup. This is the time I make green soup – 100% green vegetables. It is light, very little fat, pure chlorophyll goodness – easy to digest.     Try it, it works for me every time. 
Find the recipe in the Cooking & Recipe section.