Rules for chemical formulas (Back to search) 1  Enter a sequence of element symbols followed by numbers to specify the amounts of desired elements (e.g., C6H6). 2  Use correct case for element symbols. 3  Elements may be in any order.  If only one of a given atom is desired, you may omit the number after the element symbol.
Half of all varicella zoster cases occur in children between the ages of 5 and 9. It has been estimated that, before the chickenpox vaccine was introduced in the U.S. in 1995, only 10 percent of Americans over the age of 15 had never had chickenpox.
Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual's immune system to develop adaptive immunity to a pathogen. Vaccines can prevent or ameliorate morbidity from infection.mallpox was most likely the first disease people tried to prevent by inoculating themselves and was the first disease for which a vaccine was produced. The smallpox vaccine was discovered in 1796 by the British physician Edward Jenner, although at least six people had used the same principles years earlier.