With regards to mixing vaccines, for now, it might be safer for now that they belong to the same category of delivery system, for example, inactivated and inactivated, adenovector and adenovector, mRNA and mRNA. Experts are still trying to figure out about the benefits or consequences of mixing the vaccines across different delivery systems, like inactivated and adenovector, or adenovector and mRNA.
mRNA : Pfizer, Moderna
Adenovector: J&J, Cansino, Sputnik V, Astrazeneca
Inactivated: Sinopharm, Sinovac, Covaxin
Protein Subunit: Novavax, Anhui (forgot the name)
Astrazeneca has been considered mixing with Sputnik V. Sputnik V is unique is that first and the second shot are different vectors from each other. In other words, Sputnik V actually consists of two different vaccines.
Note that Sinopharm is also developing an adenovector and a protein subunit vaccine.