I mean, aren't the Chinese vaccines the 'old/standard' vaccines that are more understood and well researched in general?
Or like, less unknown risks in comparison to MRNA, which is still much newer and so can have a lot of unknown risks.
All vaccines for covid are new research. But China had the unique opportunity to compare, pick and choose between which type it wanted domestically.
China also produces much of all Asia's reserve of mRNA covid vaccines through Fosun, but has never approved it for use at home.
I can't exactly say how government experts made the decision, I'd have to read their papers and probably even some papers that wouldn't be publicly accessible to say why they chose inactivated, but a big reason might be that all currently theorized mRNA vaccines can only utilize, create immunity against the spike protein, which is the most mutatable part of the virus. Whereas an inactivated vaccine can provide better overall immunity even when mutations are accounted for.
The pattern we have seen so far is that mRNA can reach similar levels of protection on paper as inactivated when it comes to a single variant, and mRNA can be rolled out faster. However, when huge waves cause mutation and multiple different variants in a single outbreak, the protective power of mRNA against symptoms takes a severe nosedive. Whereas inactivated really does greatly reduce mortality into nearly nothing, despite mutations.
The "miracle" of the opening outbreak causing much fewer deaths or severe sickness in China relative to almost any other country cannot be attributed to superiority in healthcare treatment alone, because at least on paper, China does not have too amazing healthcare coverage. Then, the only explanation is that it was caused by a much more effective vaccine.
That also explains the dogged determination with which China rejected recognization of mRNA covid vaccines. Had a portion of China used less effective vaccines, it would have caused major deaths during the eventual opening.