> Yet another theory, she adds, holds that the delta variant in Japan has mutated so that it has lost the ability to replicate, pushing itself toward extinction

> Yet another theory, she adds, holds that the delta variant in Japan has mutated so that it has lost the ability to replicate, pushing itself toward extinction. How does that work? A single mutation that decreases transmissivity (anywhere between 0-100%) presumably loses out to the regular variant. So did any such mutation develop spontaneously in many viruses? Can't see how that could happen.