Wasn't the implication that the wasp's "life cycle" had two stages, with an intermediary host who has to vomit the egg substance into the "brood" host?
So Liam, Shirley Allerdyce, and Jason all got sick from direct exposure to the mammoth. Liam found the mammoth (and, yes, for whatever reason, Carrie was immune), Jason carted the mammoth into town, and then Shirley found the cooler behind the market where the mammoth was stored. Elena presumably got infected from being in the same house with a "brood host" next to the house's heating system, circulating infected air (?). I don't think these people were stung by the wasps, were they? Otherwise, wouldn't we have seen a wasp? Could this be some sort of airborne infection? Or spread through fluids?
At this point, a parasite drives the host to kill someone and vomit the egg substance into the victim's torso. It then turns that person into a brood host, as we saw with Dr. Allerdyce. But what isn't entirely clear is what happens to the intermediary host, right? Jason committed suicide knowing what he's done. Shirley had a heart attack while gorging herself at the supermarket. Elena was shot by Dan. And presumably Liam is a basket case for the rest of his life?
One of the clues was the larva that Vincent found in Stoddard's dog's intestinal tract. Was the dog eating from Stoddard's "corpse"? So these larva were in the fluid vomited up by Liam, right? The hot Sienna Guillory scientist tells Vincent that wasps don't reach sexual maturity in less that 48 hours, so he's probably fine. But at that point, isn't it all guesswork as to what happens with the life cycle after all the wasps have hatched? We're just left knowing that Vincent is probably fine. Aside from the serious burns all over his face and body, of course.