With Delta we have a highly infectious variant. With Vaccination the risk from Delta is pretty low. As Delta is running riot it tops up the protection from vaccination, or gives some protection each time it fails to kill you. Which makes it harder for a new variant to spread.
A new variant that avoids that immunity, from both vaccination and from Delta, would be catastrophic, but it is fairly unlikely to avoid all the protection. At that point it'd probably be different enough to count as SARS3.
A new variant that avoids that immunity, from both vaccination and from Delta, would be catastrophic, but it is fairly unlikely to avoid all the protection. At that point it'd probably be different enough to count as SARS3.