It is entirely possible for an allergen to not cause sensibilisation ans a consequent allergy. It is extremely rare for an allergen you are sensibilized ("alle

It is entirely possible for an allergen to not cause sensibilisation ans a consequent allergy. It is extremely rare for an allergen you are sensibilized ("allergic") to, not to cause some reaction. But the reaction may vary in strength and symptoms, especially with age and presence of irritants to the immune system. Unfortunately, some vaccines do contain those irritants as active ingredients to improve the function of the vaccine.