Background: The number of shots represented by the routine childhood immunization schedule poses a logistical challenge for providers and a potential deterrent for parents. By reducing the number of injections, use of combination vaccines could lead to fewer deferred doses and improved coverage rates.
Objective: To determine the effect of combination vaccines on coverage rates.
Methods: This was a retrospective study of administrative claims data from the Georgia Department of Community Health Medicaid program conducted from January through September of 2003. Coverage rates were compared between children who received at least 1 dose of HepB/Hib (COMVAX) or DTaP/HepB/IPV (PEDIARIX) (the combination cohort) and children who received no doses of either combination (the reference cohort). Infants with fewer than 4 vaccination visits were excluded from the analysis. Multivariate logistic regression was performed on the whole study population to assess the effect of combination vaccines while controlling for potential confounders. Hepatitis B and pneumococcal conjugate vaccine coverage rates were not included as outcomes.
Results: The study population consisted of 18,821 infants, 16,007 in the combination cohort and 2814 in the reference cohort. Unadjusted coverage rates for DTaP, IPV and the 4 DTaP:3 IPV:1 MMR, 4 DTaP: 3 IPV: 1 MMR: 3 Hib: 1 varicella, and 3 DTaP:3 IPV: 3 Hib series were higher in the combination cohort. Receipt of at least 1 dose of a combination vaccine was independently associated with increased coverage for each of these vaccines and vaccine series when controlling for gender, birth quarter, race, rural versus urban residence and historical provider immunization quality.
Conclusions: Use of combination vaccines in this Medicaid population was associated with improved coverage rates. Additional studies are warranted, including those examining private sector populations and outcomes such as timeliness and cost.