The original 1000x study (I don't know if there's been another with a number that high) was actually a measurement of viral load on first detection. This is dif

The original 1000x study (I don't know if there's been another with a number that high) was actually a measurement of viral load on first detection. This is different from straight up viral load (other papers seem to indicate that delta is more like 4x viral load at peak compared to alpha at peak). The 1000x is due to how aggressively delta variant is about to replicate. As for what the actual changes in mechanism is... I could try to summarize this (https://www.nature.com/articles/d41586-021-02039-y https://www.nature.com/articles/d41586-021-02039-y), but I think I would fail. It's a nature news article (so free access for everyone!). It's on the technical side of pop-sci.