It has, millions of times. There are machines that create RNA molecules out of the RNA sequences stored in computers. There are machines that create the proteins encoded in these RNA molecules. You can put such proteins into the nose of a mouse and they replicate and infect other mice. This can be proven by adding luciferase creating genes to the virus sequence before creating the RNA. The luciferase (firefly light) gets created in every infected cell - the mouse starts to glow. And, after some time, the mice around. Even biology students can do that, it's part of their training with biomarkers.
If it was isolated they wouldn't have to do all that. Their evidence is: look a cytotoxic effect, it must be a virus.
99.9% of the viruses living with us are symbiotic, they help the microorganisms that live with us doing digestion and helping our immune system. Only very few viruses can survive fighting our immune system every season. They can do that because our immune system cannot kill all viruses at once without killing the good guys.
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