I'm gonna start with the foundation first.
About 70% of your immune system is in your gut with your flora.(composition of bacteria) There is never an empty void in your gut. Either you are going to have a good flora(mostly good bacteria), or an unhealthy one(too much bad bacteria). You need the healthy bacteria there to eat any bad bacteria that shows up. If you don't have enough good bacteria there, bad bacteria automatically replaces it. The problem with that is it places a burden on your immune system because it has to keep fighting the bad bacteria off. In that case your immune system will never be at full capacity to fight something like the coronavirus.
Once you clean your gut out like do a detox, get your probiotics and eat clean. Most fruits and vegetables have some fibers that your body don't digest, that's what your good bacteria eats. When you eat trash food you are feeding the bad bacteria. That's why they say a bad diet feeds disease, that is literally true. Eating greasy trash food is a no go. I won't even drink liquor while this pandemic is on, it might kill too much good bacteria. So "prebiotics" or plenty of veggies will feed your good bacteria(oatmeal too, mushrooms is really good food for good bacteria)
On to Elderberry:
Elderberry has compounds that help make your cells harder for viruses to penetrate. Also it's high in antioxidants. Antioxidants help to protect your immune cells from damage. With the coronavirus, you aren't going to have any antibodies for it, so your body is going to have to fight this disease with inflammation. It creates a scenario like war when civilians are killed, therefore you need the antioxidants that are in veggies and elderberry to minimize damage and help protect your immune cells as well as others. Here is the thing, elderberry also causes your body to produce cytokines. They are proteins that the immune cells use for communication. It basically tells them to get ready for WAR. That is a good thing, it's just that with this new coronavirus they are seeing two phases of the disease. The people that stay sick long enough to cross over to the last phase are at risk for a cytokine storm. That's basically when the immune system is overactive either after it won or some other kind of way. It starts attacking good cells. That's how a significant amount of people are actually dying from this particular disease.
This also happens in other diseases and there is no evidence that elderberry has ever contributed to a cytokine storm and it's been around for a very long time. It's just that when you have a high number of cases of cytokine storms you want to just play it on the safe side. Covid 19 starts off with minor symptoms like a cold in the first phase, gives you more than enough time to stop taking elderberry and to have reaped the benefits of using it.
A tumeric supplement high in curcumin can regulate your immune system and quell a cytokine storm. It's just that the way it works is a bit foggy to me at this point. I have some and I will only consider taking it if I thought I was actually having a cytokine storm because I know it's good to help with that but I don't understand how it could help outside of that for this virus. It's a medicinal spice, I just don't really understand it yet myself.
University of Arizona reference here. It is a public research University with a medical school. Let me know if you have any questions
https://integrativemedicine.arizona.edu/COVID19/FAQ.html