Varicella vaccine from a child with natural varicella, introduced into human embryonic lung cell cultures, adapted to and propagated in embryonic guinea pig cell cultures, and finally propagated in human diploid cell cultures. Japan was among the first countries to vaccinate for chickenpox. The vaccine was first licensed in the United States in 1995. Routine vaccination against varicella zoster virus is also performed in the United States, and the incidence of chickenpox has been dramatically reduced there (from 4 million cases per year in the pre-vaccine era to approximately 400,000 cases per year as of 2005). In Europe most countries do not
Short-term memory becomes even more difficult. However, capacity of STM can be affected by the following: Influence of long-term memory, Reading aloud, Pronunciation time and Individual differences. Diseases that cause neurodegeneration, such as Alzheimer's disease, can also be a factor in a person's short-term and eventually long-term memory. Damage to certain sections of the brain due to this disease causes a shrinkage in the cerebral cortex which disables the ability to think and recall memories. Memory loss is a natural process in aging. One study investigated whether or not there were deficits in short-term memory in older adults. This was a previous