@pastanaga - It's not as simple as that. The symptoms are caused by an immune reaction, of course, but that immune reaction is intentionally triggered by the virus in order to spread itself. I mean, the virus isn't thinking, it's acting as it's been programmed to act from years of evolution.
A lot of the things people do to strengthen their immune system are pointless, as it generally functions well as long as you're healthy. Human T cells are going to function whether you eat all your garlic pills or not. But having a strong immune system is not a bad thing.