China can and should take the time to do a gradual vaccination campaign because:
1) the costs of a mass vaccination campaign and its potential benefits is not attractive right now
2) the best way to reduce COVID in china right now is to reduce the importing of COVID from other countries (therefore vaccinating other countries is the priority)
3) New variants have only gotten our attention starting in December, the science is still new on how all the vaccines, which were developed using the genetic code from feb/mar would work against multiple variants
4) Sinopharm/Sinovac represent inactivated viruses which china probably wouldn't have developed had it had the confidence in mRNA. mRNA is better if you can have the cold chains for it (which china actually does). In a few more months, china's mRNA and subunit vaccines will go on-line, which gives china the full plate of vaccine options it needs. Anything available in the west will have its domestic analogue. Some might work better, we just dont know.
5) the chances of a massive wave overwhelming china in later half of this year is incredibly remote, given appropriate levels of public education, remote technology, and government mobilization.