In adult dogs, vomiting is not some I generally get too concerned about. Once the purge whatever bothers them, they often just go about their business. It isnt always like a human who vomits when sick.
In a puppy, however, it is easy to quickly dehydrate if they cant keep anything down. Is he keeping water down? If you are concerned about him, give your vet a call, or you can call the emergency vet office and see what they suggest. You'll get quicker responses from them than you will from us here, and the advice/suggestions will have the backing of folks with known medical backgrounds!
FYI: My dogs love apple; I think most dogs do. The concern is the apple seeds and greenery; they can be poisonous for dogs. Here's some information I found on Tiggertags.com:
APPLE SEEDS:
Apple seeds are in the same category as other fruits like apples, cherries, peaches and apricots. The stems, leaves and seeds contain cyanogenic glycosides, and depending on the dose, you will see not only the common gastrointestinal effects but weakness in coordination and difficulty breathing. In some extreme cases, animals can go into shock or coma and can even result in death. The toxic ingredients are contained in the center of the seeds, so be sure keep your pet from chewing or crushing the seeds with their teeth. Another interesting thing to point out is that the level of toxicity can depend on growing conditions. If it's a stressful growing environment for an apple tree, the level of toxicity may be less than if the tree was growing in a healthy environment. This makes it difficult to gauge how much is a dangerous level.