Zhou F et al. (2005) Impact of varicella vaccination on health care utilization. JAMA 294: 797–802

Following chickenpox, the varicella zoster virus remains latent in the nervous system; its reactivation causes the neurological disorder herpes zoster (shingles). Before varicella vaccine licensing in the US in 1995, most people developed chickenpox, with ∼13,000 hospitalizations and 100–150 deaths annually. A group from the Centers for Disease Control and Prevention studied the impact of this vaccine on hospitalization and related costs.

This retrospective, population-based study used data from MarketScan® databases (MEDSTAT Group, Inc., Ann Arbor, MI) covering ∼40 employer insurance plans—about 4 million covered lives per year. The study sample included patients aged 0–49 years who had hospitalizations/ambulatory visits caused by varicella between 1994 (prevaccination) and 2002. Patients were divided into three groups: <10 years, 10–19 years and 20–49 years. Infants (<1 year), who are ineligible for vaccination, were also evaluated.

Varicella hospitalizations decreased significantly in all groups between 1994 and 2002 (P <0.001), with the greatest decline among infants. Ambulatory visits with varicella as the primary diagnosis also decreased—from 215/100,000 population in the prevaccination period to 89/100,000 in 2002 (P <0.001). Declining rates among infants and adults indicate the presence of herd immunity in the population. Hospitalization:ambulatory visit ratios decreased during the study, suggesting decreasing disease severity. Estimated annual medical expenditure from varicella decreased from US$84.9 million prevaccination, to $22.1 million in 2002.

Zhou et al. conclude that the varicella vaccination program has shown considerable success, with a dramatic decrease in varicella hospitalizations, ambulatory visits and related expenditure. As the study population was not fully representative, however, further surveillance is needed to more accurately examine the impact of varicella vaccination.