Sorry, correlated with the maximum intensity of symptoms over the course of the disease. Your viral load peaks right before you develop symptoms (generally). But viral load at peak tends to predict the severity of later symptoms and so being long-term asymptomatic is correlated with lower peak viral load. Plus, in addition to viral load, some symptoms like coughing increase transmissibility.

EDIT: I'm not saying that a vaccine that conveys protective but not sterilizing immunity means we can stop worrying about true asymptomatic transmission entirely. But I'd assume that it's enough to driver the natural R0 well below 1.0 if everyone gets the vaccine all by itself.