IIRC Chinese vaccine wasn't very effective but they were able to contain early infections so the "survivors" immunity isn't widespread either. In these conditions the consequences of a COVID wave could be quite severe, depending on which strain they're getting. Like the first wave e.g. in Italy.
I think they're fucked either way, lockdown or no lockdown. But the rationale for the lockdown could be to avoid overwhelming the hospitals. Implemented in a typical for China totalitarian fashion. I've seen reports they're exterminating pets.
Vaccines aren't supposed to prevent inflections, still, their effectiveness could be worse than the ones we have in Europe and US, but still doesn't make sense. When the pandemic started, China wasn't that paranoid about new infections, what changed now?
This situation will have serious effects in the supply chain, we were f*cked with Covid the past two years, the war hasn't stopped, and now China is implementing policies like these.
New mutation or not, it's not sensible to have such strict measures, when the rest of the Western world is easing measures.