[set fair (OP)]

I'm thinking of perhaps deleting the  furin cleavage site and one or more of the helper proteins, such as the one which enters the nucleus and turns off the alarm (preventing the presentation of viral proteins, the warning of adjacent cells and self destruction). Then seeding it in the population.

Could the Chinese have done this?

[set fair (OP)]

I edited the original post to include furin cleavage site.

From https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7457603/

SARS-CoV-2 has resulted in a global pandemic and shutdown economies around the world. Sequence analysis indicates that the novel coronavirus (CoV) has an insertion of a furin cleavage site (PRRAR) in its spike protein. Absent in other group 2B CoVs, the insertion may be a key factor in the replication and virulence of SARS-CoV-2. To explore this question, we generated a SARS-CoV-2 mutant lacking the furin cleavage site (ΔPRRA) in the spike protein. This mutant virus replicated with faster kinetics and improved fitness in Vero E6 cells. The mutant virus also had reduced spike protein processing as compared to wild-type SARS-CoV-2. In contrast, the ΔPRRA had reduced replication in Calu3 cells, a human respiratory cell line, and had attenuated disease in a hamster pathogenesis model. Despite the reduced disease, the ΔPRRA mutant offered robust protection from SARS-CoV-2 rechallenge.

Looks like this might be a candidate.

If China has done this, there should be a tell tale signature in antibodies produced. It would explain why they aren't rolling out sinovac across the country.