Do you think there needs to be a minimal amount of venom or a specific concentration of it to turn someone?
My thought was that a single bite is enough to turn an adult and since Twilight vampires don't have fangs that directly inject the venom it must be the little amount of saliva that's on their teeth that does it. So you dont need much but could one vampire spit into a town's water supply and turn a bunch of people that way?
Granted, it'd be a horribly inefficient way of doing it IF it works in the first place (the person needs a cut or other small injury for the venom to enter the bloodstream, no control over who turns and who doesn't, you might end up with 20 newborns at once and have the volturi come after you etc.) but the potential for chaos is so delicious. Also it'd be really funny if that inspired another law: 1. keep the secret 2. no immortal children 3. don't spit into a town's water supply, you nasty people.
Partially answered: less venom injected simply means longer incubation time. This is the case with real life viruses too, and where it entered the body can also impact incubation period.
I think, judging by the fact that this hasn't happened in canon, there are no records of people turning into vampires without being bitten, venom probably doesn't survive very long on its own or when exposed to elements that are not a human.
Carlisle did invent syringes for Breaking Dawn, but we don't know what material those were made of, how long they'd been sitting when Edward used them nor, crucially, if they actually worked. Edward bit Bella everywhere he could manage in addition to using the syringes, it could be the venom in the syringes had already died or lost potency by that time and Bella was turned from the bites alone. Carlisle, who was on a time crunch with limited resources, would not have had an opportunity to test these.
In other words, we know from people only becoming vampires in canon from direct exposure that venom can't survive on its own, and the syringes don't prove that venom could survive under certain conditions because we don't actually know that those syringes were potent.
Fascinating question, anon! Know that there was a lot of virology babble in this post that I had to delete upon remembering I had no idea what I was talking about.









