Influenza Immunization Among Medicaid Enrollees in New Hampshire

Background: Influenza is a contagious respiratory illness that can cause mild to severe illness, and at times lead to death. New Hampshire (NH) provides vaccines, including influenza vaccine, at no cost to children age ≤18 years. Providers can bill third party payers, such as Medicaid, for vaccine administration. The Advisory Committee on Immunization Practices recommends annual vaccination of children age 6 months through 18 years with influenza vaccine.

Objectives: There are limited data on the specifics of influenza immunization among NH children, and no county-specific data. To learn more about influenza vaccine coverage among Medicaid enrollees, we analyzed influenza billing data from the NH Medicaid Database.

Methods: We identified vaccine recipients aged 1–18 years using Current Procedural Terminology (CPT) codes for influenza vaccine administration. Data were gathered for 12-month periods, between July 1^st and June 30^th, including years 2004-2009. Using the overall enrollments as of July 1^st, we calculated percentages and 95% confidence intervals for influenza immunizations by influenza season, age, gender, and county of residence.

Results: Influenza immunization among NH Medicaid members has gradually increased from 5.8% during 2004/05 to 14.5% during the 2008/09 season. There is no difference between genders; and influenza immunization decreased with the increasing age. There are statistically significant differences by county, and these differences are consistent over the years. County specific estimates ranged from 1.7% to 8.5% in 2004/05, and from 5.8% to 18.3% in 2008/09.

Conclusions: The Medicaid database is a readily available data source of potentially valuable information about vaccination. However, some NH providers were not reporting the administration codes until 2008, when a mandate to use CPT codes went into effect. Whether under-reporting or other factors influenced the observed geographic variability needs to be explored. Nevertheless, the recent overall changes and differences are similar to those observed during previous seasons.