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.
Initially, the terms vaccine / vaccination referred only to smallpox, but in 1881 Louis Pasteur proposed that to honour Jenner the terms be widened to cover the new protective inoculations being introduced.nother early account was Dr John Fewster 's 1765 paper on Cowpox and its ability to prevent smallpox read to the London Medical Society. He reported that variolation induced no reaction in persons who had had cowpox. Fewster was a contemporary and friend of Jenner.