18 month old got her vaccines that were due and a flu shot 10 days ago. now she is breaking out in hives. no symptoms or diet change. related?

Delayed reaction: Your child may be having a delayed allergic reaction. You can use Benadryl (diphenhydramine) to control the hives.

See pediatrician: Benadryl (diphenhydramine) best avoided in children. Sometimes makes them crazy. There are much better antihistamines. Probably this will resolve in a short lime.

Possible: It is usually not the killed virus itself but what may be added to the vaccine which can cause an allergic reaction. For example, some vaccines do contain small amount of gelatin to which a few people may have become allergic.