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Hospitalizations because of chicken pox down dramatically since implementation of vaccine

August 17, 2005

Since the introduction of the varicella (chicken pox) vaccine in 1995, hospitalizations and doctor visits because of chicken pox have dropped dramatically, according to a study in the August 17 issue of JAMA.

Varicella vaccine is recommended for routine immunization of children aged 12 to 18 months and for older susceptible children and adults in the United States, according to background information in the article. Before its licensure in 1995, almost everyone developed chicken pox; thus, incidence approximated the birth cohort, with about 13,000 hospitalizations and 100 to 150 deaths annually. Varicella vaccine coverage has increased steadily, reaching 81 percent in 2002 among children aged 19 to 35 months nationally, while varicella disease incidence has declined in all age groups. However, data documenting the impact of vaccination on varicella-related health care utilization have previously been limited.

Fangjun Zhou, Ph.D., M.S., of the National Immunization Program, Centers for Disease Control and Prevention, Atlanta, and colleagues conducted a study to determine the patterns of hospitalization and ambulatory visits for chicken pox and their associated medical expenditures in the United States, evaluating these factors beginning in 1994 (before availability of varicella vaccine) through 2002 (7 years after vaccine licensure). Data included enrollees (children and adults) of more than 100 health insurance plans of approximately 40 large U.S. employers.

The researchers found that from the prevaccination period to 2002, hospitalizations due to chicken pox declined by 88 percent (from 2.3 to 0.3 per 100,000 population) and ambulatory visits declined by 59 percent (from 215 to 89 per 100,000 population). Hospitalizations and ambulatory visits declined in all age groups, with the greatest declines among infants younger than 1 year. Total estimated direct medical expenditures for chicken pox hospitalizations and ambulatory visits declined by 74 percent, from an average of $84.9 million in 1994 and 1995 to $22.1 million in 2002.

"The data in our study demonstrate the substantial success that the varicella vaccine program has shown since it was implemented 10 years ago. However, nationally representative data are needed to more accurately monitor the impact of the varicella vaccination program. The Council of State and Territorial Epidemiologists has recommended that states now begin to conduct case-based surveillance," the authors conclude.

JAMA and Archives Journals