Varicella vaccine were vaccinated as children were still protected from varicella." However, since only one out of five Japanese children were vaccinated, the annual exposure of these vaccinees to children with natural chickenpox boosted the vaccinees' immune system. In the United States, where universal varicella vaccination has been practiced, the majority of children no longer receive exogenous (outside) boosting, thus, their cell-mediated immunity to VZV (varicella zoster virus) wanes—necessitating booster chickenpox vaccinations. As time goes on, boosters may be necessary. Persons exposed to the virus after vaccine tend to experience milder cases of chickenpox. Catching "wild" chickenpox as a child has been
Psychogenic disease to be psychogenic include psychogenic seizures, psychogenic polydipsia, psychogenic tremor, and psychogenic pain. There are problems with the assumption that all medically unexplained illness must have a psychological cause. It always remains possible that genetic, biochemical, electrophysiological, or other abnormalities may be present which we do not have the technology or background to identify. The term "psychogenic disease" is often used in a similar way to "psychosomatic disease". However, the term "psychogenic" usually implies that psychological factors played a key causal role in the development of the illness. The term "psychosomatic" is often used in a broader way to describe