Varicella Vaccination Reduces Hospitalizations

Norra MacReady

January 11, 2011

January 11, 2011 — The rate of varicella-related hospitalizations has declined dramatically since universal vaccination began in 1995, investigators declared in an article published online January 3 and in the February print issue of Pediatrics.

The data suggest that varicella vaccination may have prevented as many as 50,000 hospitalizations between 2000 and 2006 compared with the "prevaccination era" (1988 - 1995), along with a corresponding decrease in direct medical costs for associated illnesses, the authors said.

Routine varicella vaccination began with a single-dose program in 1995. By 2005, surveys were showing a decrease in the incidence of varicella ranging from 53% to 94% compared with the prevaccination era. During the 1-dose vaccination era (ie, 2000 - 2006), varicella vaccination coverage exceeded 65%. The rollout of a 2-dose regimen, in which children received the first vaccination at 12 to 15 months of age and the second at age 4 to 6 years, took place in 2006.

In an effort to characterize more thoroughly the trends in hospitalization associated with the single-dose vaccine, lead author Adriana S. Lopez, MHS, and colleagues from the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention in Atlanta, Georgia, analyzed data from the National Hospital Discharge Survey (NHDS) from 1988 to 2006. During that time frame, NHDS collected data on roughly 270,000 people from approximately 500 hospitals. The researchers also analyzed data from 1998 to 2006 from the Nationwide Inpatient Sample, which includes information on 5 to 8 million discharges per year from approximately 1000 hospitals around the United States.

Varicella-related hospitalizations were identified using International Classification of Diseases, Ninth Revision, Clinical Modification, codes for varicella, complications of varicella, varicella pneumonitis, or postvaricella encephalitis. Patients were placed into 1 of 3 categories: "(1) having no comorbid or immunocompromising condition, (2) having a comorbid condition (eg, diabetes or cardiac disease), or (3) immunocompromised (eg, HIV or cancer)."

From the NHDS data, the authors estimated that there were, on average, 10,632 varicella-related hospitalizations per year during the prevaccination era compared with 3498 hospitalizations annually during the 1-dose era (P < .01). When the authors employed a more restrictive analysis and looked only at hospitalizations listing varicella as the principal discharge code, they calculated an average annual estimate of 2912 varicella-related hospitalizations in the 1-vaccination era compared with an average of 8680 hospitalizations annually during the earlier period (P < .01).

All in all, they write, the NHDS data showed that annual varicella-related hospitalizations decreased by more than 70% in all age groups younger than 20 years, and by 65% in the 20-years-and-older group between the prevaccination and 1-vaccine eras (P < .001 for trend). The incidence of varicella was highest in children in the 0-to-4-years age groups in both time periods, but the vaccine program was associated with a 72% drop (P < .001 for trend).

Toddlers up to age 4 years also had the highest hospitalization rates related to varicella, according to the Nationwide Inpatient Sample data, but the 1-vaccination era saw a decrease of 70.1% (P < .001). Rates for patients aged 20 years or more dropped by 50% (P < .001). The lower hospitalization rates seen in both data sets for all age groups should quell concerns that universal vaccination of children might shift the disease burden to older patients, in whom the illness is more serious, the authors pointed out.

"Results from analyses of hospital discharge codes must be interpreted with caution because diagnostic codes for varicella could have been misattributed or inadvertently excluded," the authors warned. For example, hospitalized patients with herpes zoster may have been miscoded as varicella. Another limitation is that hospital discharge data do not contain much information about disease severity and reason for hospitalization. Finally, the decrease in hospitalization resulting from the vaccine was so marked that "we were limited in the analyses we could perform using NHDS and could not estimate varicella-related hospitalization rates in children younger than 1 [year] or age-specific rates of complications."

Varicella incidence and associated hospitalizations should continue to decline, now that the 2-vaccine program is in force, the researchers concluded.

This work was presented in part at the annual meeting of the Infectious Disease Society of America, October 21 to 24, 2010, Vancouver, Canada The authors have disclosed no relevant financial relationships.

Pediatrics. Published online January 3, 2011.

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