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
Foreign animal disease holdings are essential." Rinderpest Rinderpest Teschen disease Teschen disease Screwworms New World Screwworms Foreign animal disease A Foreign animal disease (FAD) is an animal disease or pest, whether terrestrial or aquatic, not known to exist in the United States or its territories. When these diseases can significantly affect human health or animal production and when there is significant economic cost for disease control and eradication efforts, they are considered a threat to the United States. Another term gaining preference to be used is Transboundary Animal Disease (TAD), which is defined as "those epidemic diseases which are highly contagious or transmissible