Season 1 Episode 16 of "Fringe" features a creature that stings you. The stinger is left behind along with offspring in the form of maggots. One of the already dead people is nearly completely eaten in 24 hours. Agent Francis is infected with a sting and they poison him to try and kill the creatures, but they start eating him and keep growing. At some point we see massive maggots moving beneath his skin. Wouldn't they have caused enough damage to kill him? I mean they were already eating on him for nearly 24 hours. Even if their eating were slowed down they still would have eaten a good portion of Francis. Instead they inject Francis with the blood of the beast and this somehow cures him. In fact, when they ultrasound him again it appears that the maggots are back to miniature size!
Without watching the episode again before answering, you seem to have covered most of the plot points in your actual question. Although there are no reasons I can find to Charlie surviving, it seems mostly based on him being a main character in the show. If larvae didn't eat vital organs and only muscle protean and fatty tissues and were killed before they ate too much it wouldn't be inconceivable to survive the experience.
The cure however I remember being more of a treatment that suppresses the "Chimera" offspring from beginning their growth cycle and killing Charlie which he has to take daily. Its based on the Chimera blood collected by Walter that essentially makes the dormant larvae think they are still within the mother waiting to be deposited. The size remission could just be down to them being an entirely new breed of creature and that they might regress to a smaller size due to metabolism or shedding of weight to hibernate while dormant? Or just that the bigger more active ones have broken down due to the 'cure', it's quite speculative at best I'm afraid. The Wiki is more of a episodic list of plot but this is the link to the page on the episode.
The other victims spent 24 hours without any medical assistance, so the maggots grew very fast.
Charlie Francis, on the other hand, was poisoned, as you say, just after the sting. It did not kill the maggots, but it slowed down their growth. That's why he could survive until he was injected with the blood of the beast.