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
Motor neuron disease Motor neuron disease Motor neuron diseases (MNDs) are a group of neurodegenerative disorders that selectively affect motor neurons, the cells which control voluntary muscles of the body. Commonly, the following disorders are counted among motor neuron diseases: The term “motor neuron disease” sometimes refers to ALS, but in this article, the term refers to a group of diseases listed above, which includes ALS. Motor neuron diseases affect both children and adults. While each motor neuron disease affects patients differently, they all cause movement-related symptoms, mainly muscle weakness. Most diseases seem to occur randomly without known causes, but some forms are