I'm stumped they didn't consider buying other vaccines. Maybe they don't want to be reliant on the west. They're indeed doing a mistake keep the lock strategy...
You know how some old people believe all sorts of conspiracy theories about the government? Because their government was actually evil during their lifetime, it becomes much harder for them to believe that this one time the government really does want to give them medicine for their own good.
I have relatives in Bulgaria, a country with full access to all western vaccines thanks to EU but is among the least vaccinated countries in the world and among the top deaths of COVID-19 per capita.
I was shocked when I visited Bulgaria once travel become possible. Everyone knew someone dead but they also were telling stories about this one person who went to get a vaccine and their veins turned blue and died shaking. People in villages were tellings tories how Bill Gates will monitor them or that the virus and the younger ones were saying that the vaccines are a sham and the governments orchestrated it to reduce the population(Bulgaria is also a top country in population decline, the government and EU are actually trying very hard to increase the population).
When people want to believe things, they believe things.
The CCP may not be the Kiwanis Club but they're not the Legion of Doom either. It's not a democracy but they still need some degree of popular support, and letting everyone's grandparents die is not a great way to engender it.
In any case there are multiple paths available and so far they seem stuck on the failing one. It's strange.
People in China are still posted about that.
I think it's easier to gain this information via hacking and data theft or paying insiders for documents than actually reversing the vaccine.