Effect of combination vaccines on completion and compliance of childhood vaccinations in the United States

Vaccination at age-appropriate intervals increases protection against morbidity and mortality; however, compliance rates among children remain low partly due to a complicated vaccination schedule. Use of combination vaccines reduces the number of injections per visit; however, there is limited evidence quantifying the effect of combination vaccines on vaccination rates. To examine how combination vaccines impact childhood completion (receipt of recommended doses) and compliance (receipt of age-appropriate vaccinations) rates, this study analyzed vaccination data from the 2012 National Immunization Survey (NIS), a nationally representative cross-sectional survey of caregivers of children aged 24 to 35 months in the United States. Vaccines were categorized as combination or single antigen. Vaccine completion was measured at ages 8, 18, and 24 months. Vaccine compliance and time undervaccinated were measured at 24 months. Children who received at least 1 combination vaccine (86%) had a higher completion rate (69%) and compliance with the full vaccine series (4:3:1:3:3:1:4 series) at 24 months (24%) than those who received only single-antigen vaccines (50% and 13%, respectively). Receipt of combination vaccine was associated with an increased likelihood of completing all recommended vaccinations at 24 months (odds ratio [OR] = 2.5; P < 0.001), receiving all vaccinations at age-appropriate times (OR = 2.2; P < 0.001), and less than 7 months undervaccinated (OR = 2.4; P < 0.001). Combination vaccines were associated with improved completion and compliance and should be encouraged among children who are undervaccinated or who received single-antigen vaccines only.