I have an uber healthy fully vaccinated 3yo . He's been sick before, no doubt. He's also in full time daycare so exposed to a crapload of germs (I work, if I didn't we would be homeless). He rarely gets antibiotics, and is only allergic to carpet which he inherited from me. He would probably be just as healthy if he were unvaxed, and probably would have gotten all the same illnesses (colds and stomach bugs).