Is there a plausible universe where a bunch of people got Omicron *instead of* Delta, decreasing the [new] case count for Delta as the case count for Omicron rose?
Why not? Someone gets infected with Delta on Monday and with Omicron on Thursday. This would be a Delta case on Friday, but Omicron outcompeted Delta inside the body, and now it's an Omicron case instead.
Is there a plausible universe where a bunch of people got Omicron *instead of* Delta, decreasing the [new] case count for Delta as the case count for Omicron rose?
In the long run, absolutely. Over the week? No.
Why not? Someone gets infected with Delta on Monday and with Omicron on Thursday. This would be a Delta case on Friday, but Omicron outcompeted Delta inside the body, and now it's an Omicron case instead.
Why does it matter? Because people over at metaculus had points riding on this thing. Gotta keep our priorities straight, here.
Reading this post only now, feel free to ignore my comment on your previous post on WP because this post essentially answers the comment.
The nowcast data being bad seems plausible, though it's a shame because the world in which it is accurate would have been much more interesting :)