The varicella (chickenpox) vaccine is given to children 12-18 months old and has a protective factor for younger children.

A review of data from 1995 to 2008 showed a nearly 90% decline in the incidence of chickenpox in children age 0 to 11 months old, those too young to receive the vaccine. There was also a significant decline in the severity of symptoms as the vaccine became more widely used.

One cause of this change in incidence could be “herd immunity.” The concept is that if enough members of a “herd” (population) are immune to a disease, then the chances that herd members without immunity decreases. Another possible explanation is that more mothers have received the vaccine and they pass their immunity on to their babies.

Pediatrics, 12/11

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From issue: 28/03-04