How can a virus mingle with more virulent strains? A virus isn't a live entity that can co exist with other forms of virus to alter their form.
The only way a virus will mutate away from the natural trend as more infectious and less virulent to being more virulent is when people are injected so that they can still get that virus and pass it on but have a reduced reaction. That could cause a mutation to overcome the unnatural response and it's also a no no to 'vaccinate' during a pandemic because of that high risk.
