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 against measles was introduced in 1968. The measles antigen was combined with mumps and rubella with the introduction of the combined MMR vaccine in 1988. Increased incidence of measles in 1994 prompted mass school vaccination with measles and rubella (MR) vaccine for all children aged five to 16 years.A second dose of MMR was introduced for pre-school children in 1996, as a one dose programme would not support eventual measles elimination.ncreased incidence of measles in 1994 prompted mass school vaccination with measles and rubella (MR) vaccine for all children aged five to 16 years. A second dose of MMR was introduced for pre-school children in 1996, as a one dose programme would not support eventual measles elimination.