I took my kitten to a vet location because I noticed that he wouldn't eat for the past day and he threw up this morning with what seem a flat worm. I took him to the location to get a dewormer centrid shot. It's been about 12 hours and he's still not eating but he's drinking water and he's also walking with a hunch and cries/meows every time I try to pick him up. I'm wondering if that's the reason why he hasn't been eating and if it is when would he start been healthy again? Thank you.

It is possible that the worms were the reason why he wasn't eating, and the deworming treatment itself can make him feel nauseous and unwell. It's the result of the dead worms moving through his GI system. I would recommend offering him a bland diet of boiled white meat chicken (no bones) in small amounts to try to tempt him to eat. You can also soak his dry food in tuna juice, or offer him gently warmed really smelly wet food, such as sardine or fish based. If he still isn't eating in the morning, I would have him seen by the vet again. It will take at least two deworming treatments to kill all the worms.

It should be fine, but depending on the type of medication you have and type of worm, he may still need a dewormer. You can request one tomorrow. It will likely need to be repeated in 2-3 weeks anyway. Better yet, submit a stool sample to diagnose intestinal parasites.