They know this vax protects some people, but it also kills some and makes some others die ... Soon?
So they secretly vaccinated their population in early 2019. (Their citizens are already accustomed to obediently doing whatever government requires.)
At that point they were ready to let the virus out to run through the locals (with minimal impact) and then to the world. In fact they may have only vaxd Wuhan, and planned to lock them down and trap them unless they were headed out to other countries.
Then all they had to do was sit back and control their puppets.
Add to this that Wuhan was the pilot city for 5G roll out in China. The speculation is that 5G at the correct frequency induces cells in the body to undergo electroporiation (the opening of pores in cell walls) through which the a foreign entity, like a virus, can enter the cell.