Immunity-The quality or state of being immune especially : a condition of being able to resist a particular disease especially through preventing development of a pathogenic microorganism or by counteracting the effects of its products.
"Naturally acquired active immunity occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response. Once a microbe penetrates the body's skin, mucous membranes, or other primary defenses, it interacts with the immune system." source - https://courses.lumenlearning.com/boundless-microbiology/chapter/classifying-immunities/
How is this an asspull if Giorno counteracted the effects of Purple Haze?