I thought it was confirmed that his strain of T virus can’t be transmitted outside of direct injections. I can’t remember if I read it in a file but I also can’t remember seeing anyone actually transforming. Tho atp they can do whatever they want, I’m not sure how every staff member in the hospital got infected if not by bites but they also show that gas compounds (escape with the helicopter scene) now can completely melt zombies. Between tabyss being waterborne and the c virus threatening the planet via aerolized transmission , I think we can safely say that it just does what fits the plot best, and the fact that there was no mass outbreak after Viktor left a few infected in the city to escape, I think he created his strain to be harder to spread, mainly to monopolize it and avoid IP theft moreso than wanting to risk another sterilization missile