The Number of Hospitalizations Due to Chicken Pox are Down Dramatically

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 Aug. 17, 2005 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 healthcare utilization have previously been limited.

Fangjun Zhou, PhD, MS, of the National Immunization Program at the Centers for Disease Control and Prevention (CDC), 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 (seven 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 pre-vaccination 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.

In an accompanying editorial, Varicella Vaccine, Cost-effectiveness Analyses, and Vaccination Policy, Matthew M. Davis, MD, MAPP, of the University of Michigan, Ann Arbor, comments on the study by Zhou et al.: these findings do not conclusively confirm that childhood varicella vaccination is as cost-effective as originally anticipated, for several reasons. First, the cost of the vaccine has increased more than $10 per dose in inflation-adjusted terms since 1995 (the current public sector price per dose is $52.25), although an increase of this magnitude was not anticipated to change the cost-effectiveness dramatically. Second, the national varicella vaccine recommendation prompted states to measure and react to varicella as a reportable vaccine-preventable illness. The costs of such monitoring and of responding to outbreaks of varicella (e.g., in day care or school settings) may be substantial and were not included in the original analysis [in another study].

Third, and perhaps most important, there is great uncertainty about the extent to which parents and other adults experienced reductions in lost work time attributable to varicella. As with other childhood and adolescent vaccines that have recently been recommended (e.g., pneumococcal and meningococcal conjugate vaccines), indirect cost savings with varicella vaccine were expected to be larger than savings in direct medical costs.

To maximize the benefits of vaccines for children and adults in the future, it is imperative to formally and openly consider how best to incorporate cost-effectiveness considerations into deliberations about vaccine recommendations, thereby acknowledging that health and economics cannot be teased apart. From the perspectives of patients, payers, clinicians, and public health officials, costs are just as much a part of vaccines as their benefits, Davis concludes.

References: JAMA. 2005; 294:797802 and JAMA. 2005; 294:845846

Source: American Medical Association (AMA)