About 20 percent of children will have some soreness at the site of the injection. About 10 percent will have a low-grade fever. About 4 percent will have a mild rash (around ten chicken pox—like blisters).
Fewer than one in a thousand will have a seizure caused by high fever. Though these febrile seizures may seem scary, they're almost always harmless for the child. But you should call your doctor right away if your child has one.
Severe allergic reactions are rare but possible with any vaccine. See what our expert says about how to tell whether your baby's having an adverse reaction.