As I have been unable to uncover ANY scientific research regarding the effects of mixing the Sinovac and Astra Zeneca vaccines, I am extremely hesitant to reduce myself to absolute guinea pig levels.
As much as I want to receive a vaccination, I cannot assume that this is a safe combination, and also note Sinovac's poor reputation with regard to fighting off the Delta variant of the Covid virus.
Initially, I thought "any vaccine is better than no vaccine", but now I am not so sure. All things being equal, I think it best to mask up, social distance, wash hands, etc and wait for a vaccine that has been tested to be both safe and effective.