Laura E. Happe, PharmD, MPH; Orsolya E. Lunacsek, PhD; Gary S. Marshall, MD; Tamara Lewis, MD, MPA, MPH; and Shannon Spencer, RN
Childhood vaccines are among the top 10 public health advances of our time,1
resulting in the eradication of disease, decreases in mortality, and cost savings.2,3
The 2007 Harmonized Childhood and Adolescent Immunization Schedule recommended by the Advisory Committee on Immunization Practices (ACIP) provides a guide for vaccination against 14 diseases during the first 2 years of life.4
As many as 24 separate shots may be administered to a child by age 2, with many visits requiring multiple injections. This vaccination schedule presents a burden to patients and practitioners. The number of shots may be associated with discomfort for the parent and child, logistical challenges for the pediatrician and family practitioner, and ultimately deferral of recommended immunizations.5,6
Despite these challenges, immunization rates in the United States remained at or near all-time high levels in 2005.7
Coverage rates of 76%, however, leave a considerable percentage of children in the United States not receiving all of their recommended immunizations and, therefore, at risk for disease.7
More than 90% of America's managed care health plans report immunization coverage rates for their insured populations to the National Committee for Quality Assurance (NCQA). Based on the Health Plan Employer Data and Information Set (HEDIS) criteria, a set of standardized and objective measures developed by NCQA, plans report the percentage of children turning 2 years of age who have received the complete recommended immunization series according to administrative claims and chart review data (HEDIS childhood immunization measure). Among reporting commercial plans in 2005, the childhood immunization coverage rate was 77.7% for the HEDIS Combination 2 series (4 doses of diphtheria, tetanus, acellular pertussis vaccine [DTaP]; 3 doses of inactivated polio vaccine [IPV]; 1 dose of measles, mumps, and rubella vaccine [MMR]; 3 doses of Haemophilus influenzae
type b conjugate vaccine [Hib]; 3 doses of hepatitis B vaccine [HepB]; and 1 dose of varicella vaccine),8
indicating suboptimal coverage for approximately one quarter of all children.
Coverage rates, however, are not the only measure of quality. Immunization timeliness, or age-appropriate immunization, is another important measure of immunization delivery. This concept refers to the administration of each specific vaccine dose within the age range specified by the harmonized schedule. Failure to receive immunizations within the recommended age ranges may make achieving optimal protection difficult, leaving children at risk for disease. Immunization timeliness is particularly important for vaccine-preventable diseases such as pertussis. Of 10 650 children with pertussis from 1990 to 1996, fewer than half were found to have received their DTaP immunizations on time.9
Recent data reveal a potential problem with immunization timeliness in the United States. One study using data from the National Immunization Survey (NIS) showed that only 26% of children received the recommended immunizations within the specified age ranges,10
uncovering a significant need for improving immunization timeliness. On-time immunizations have also been shown to positively predict the completion of the vaccine series,11
potentially leading to improved coverage rates.
A potential solution to the increasingly crowded immunization schedule and the challenges of vaccine delivery is the use of combination vaccines, products that deliver multiple antigens in single injections. Combination vaccines have the potential to minimize patient discomfort, decrease logistical challenges, reduce extra healthcare visits, and decrease costs. As far back as 1999, the ACIP expressed a preference for the use of combination vaccines as a way to overcome the challenges of multiple injections12
; however, limited empirical data exist to quantify the effect of combination vaccines on immunization coverage rates and timeliness. The objective of this study was to evaluate the impact of a pentavalent vaccine on childhood immunization coverage rates and timeliness in a managed care organization. SelectHealth is a subsidiary of Intermountain Healthcare, a not-for-profit integrated healthcare system in Utah. SelectHealth has more than 460 000 enrollees. Due to product availability and uptake of the combination product, SelectHealth members were an ideal population in which to study the effect of a combination vaccine on immunization quality.METHODSStudy Design and Data Source
A retrospective matched cohort study was conducted utilizing encounter data (administrative claims combined with immunization registry records) from SelectHealth. The study vaccine was a DTaP, HepB, and IPV combination (DTaP/ HepB/IPV [Pediarix, GlaxoSmithKline]) that entered the US market on January 1, 2003. The vaccine fits into the recommended schedule for administration at 2, 4, and 6 months of age for a potential decrease of up to 5 injections. Because practices and providers in the SelectHealth network had immediate access to and reimbursement for the product, uptake was rapid, with substantial utilization occurring as early as March 2003.
Administrative claims data were extracted from the billing records of SelectHealth. These data were then cross-referenced using a unique patient identification number assigned to each member by the Utah Statewide Immunization Information System, a voluntary statewide immunization registry. The resultant encounter data provided consolidated patient immunization histories across multiple providers and vaccine delivery sites, including the date of vaccine administration and corresponding Current Procedural Terminology (CPT) code indicating the product administered. These data were used to assess immunization coverage and timeliness, as described below. The study was conducted in compliance with the Health Insurance Portability and Accountability Act and the study was approved by the New England Institutional Review Board.Patient Selection
Infants born between January 1, 2003 (date of study combination vaccine market entry) and October 1, 2003 (last date of data abstraction to provide 2 years of follow-up) with continuous enrollment in SelectHealth for 24 months were eligible for inclusion. Continuous enrollment in the health plan was required to increase the likelihood that all vaccines administered were captured in the encounter data. Gaps in enrollment of longer than 7 days were considered to be disruptions in continuous enrollment and rendered children ineligible for the study. In addition, to allow for an equal opportunity for immunization at baseline, a minimum of 4 immunization-related office visits were required for study inclusion.
Eligible children were stratified into 2 cohorts: the combination cohort and the reference cohort. The combination cohort consisted of children who received at least 1 dose of DTaP/HepB/IPV. Children who did not receive DTaP/HepB/ IPV were assigned to the reference cohort. Receipt of other combination vaccines (eg, Hib/HepB or DTaP/Hib) did not affect eligibility; these children were placed in the combination or reference cohort as determined by receipt of DTaP/HepB/IPV.
Demographic factors including maternal marital status, race, socioeconomic status, and infant's sex have been shown to influence coverage rates and timeliness and have been controlled for in previous analyses.10,13
Thus, children from the reference cohort were matched 1:1 with children from the combination cohort based on demographic characteristics. The matching criteria included sex, rural versus urban residency, date of birth within 30 days, and historical provider coverage within 5%. Historical provider coverage was defined as the coverage rate for the HEDIS Combination 2 series in 2001 for the provider of each child included in the study. This factor was included as a matching characteristic to minimize the effect of the provider's immunization practices on the outcome. Other demographic data such as race, maternal marital status, and socioeconomic status were not available.OutcomesCoverage Rates
. Coverage rates were calculated as the proportion of children who received at least the required number of doses for each vaccine series by 24 months of age, as recommended by the 2003 harmonized schedule.14
The number of vaccine doses for a given vaccine series was obtained by taking a simple frequency count of the vaccine doses received for each child by 24 months of age. Coverage rates were determined for the HEDIS Combination 2 series as well as each individual vaccine series. The vaccine series assessed and number of vaccine doses required to be classified as covered are described in Table 1
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