Varicella zoster virus infections in children after the introduction of live attenuated varicella vaccine

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Abstract
Varicella zoster virus is the cause of both varicella (chickenpox) and herpes zoster (shingles). A live attenuated varicella vaccine was developed in 1974 and was approved in 1995 by the United States Food and Drug Administration for administration to both healthy children (>12 months of age) and adults who are susceptible to varicella. Many studies have shown varicella vaccine to be highly effective. Widespread use of the varicella vaccine in the United States has led to important changes in the epidemiology of the infection. The purpose of this review is to summarize the most recent and important findings regarding the impact that the widespread use of varicella vaccine has had on the epidemiology of varicella zoster infections in children. Data from the United States Centers for Disease Control and Prevention have shown a dramatic decline in the incidence of varicella (76 to 87% from 1995 to 2000), with the greatest decline observed in preschool children, as well as a reduction in the number of hospitalizations for cases of varicella. However, as the proportion of children in the United States who have received the varicella vaccine has increased there have been several recent reports in which the effectiveness of the vaccine was substantially lower than expected. In particular, reports during outbreaks of varicella in children have noted increases in breakthrough disease in children who were vaccinated before the age of 15 months, in children with asthma, in those who received the varicella vaccine soon after the measles, mumps, and rubella vaccine (<28 days), and in children who received the vaccine more than 3 years before the development of disease. Although reports of outbreaks of chickenpox in highly immunized groups have raised questions regarding the need for changes to the current vaccination policy, data undeniably indicate that immunization with varicella vaccine has been and continues to be successful in reducing the burden of disease in children and that universal immunization should continue to be a priority in the United States