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 1803, used by British physician Edward Jenner for the technique he devised of preventing smallpox by injecting people with the cowpox virus (variolae vaccinae), from vaccine (adj.) pertaining to cows, from cows (1798), from L. vaccinus from cows, from vacca cow (bos being originally ox, a loan word from a rural dialect ...