The immune system is also layered - a single viral infection won’t necessarily kill you right away. If it does penetrate the initial layers, the immune system w

The immune system is also layered - a single viral infection won’t necessarily kill you right away. If it does penetrate the initial layers, the immune system will continue adapting and fighting it on each new front. Eventually your entire body might even engage using things like a fever. In this way, it doesn’t need to be right initially billions of times, but capable once at one of many steps.