But what’s the theory then? If there was a widespread milder version of covid going around in places long before the deadly one took hold, then the newer deadli

But what’s the theory then? If there was a widespread milder version of covid going around in places long before the deadly one took hold, then the newer deadlier strain would still have to be transmitted into each region separately. I don’t think it’s feasible that the mild strain spread globally and then flipped a switch and turned much deadlier all around the globe.