Learning Objectives for this Presentation:
By the end of the presentation participants will be able to:
1) understand when children are likely to fall behind in their vaccinations
2) identify the primary causes for falling behind
2) understand the importance of preventing children from falling behind in their vaccinations

Background:
Little is known about when – and why – children fall behind in their recommended vaccinations.

Objectives:
We examine vaccination status throughout the first 2 years of life, identify vulnerable transition periods that account for substantial attrition, and examine whether children fell behind because they missed vaccination visits or missed opportunities for simultaneous vaccination.

Methods:
Vaccination histories for 27,403 children aged 24-35 months in the 2005-2006 National Immunization Survey were analyzed to determine vaccination status throughout the first 2 years, focusing on milestone ages of 3, 5, 7, 16, and 19 months; percentage of children who fell behind between milestones; proportion of children who fell behind due to missed visits compared to missed opportunities for simultaneous vaccination.

Results:
The percentage of children who fell behind from one milestone age to the next ranged from 10% during the 16-19 month interval to 20% during the 7-16 month interval. Most children who fell behind during the 5-7 and 16-19 month intervals did not have a vaccination visit; half of children who fell behind during the 3-5 month interval and 85% of children who fell behind during the 7-16 month interval had a visit but missed an opportunity for simultaneous vaccination.

Conclusions:
Missed vaccination visits and missed opportunities for simultaneous vaccinations must both be addressed to reduce the number of children falling behind in their vaccinations. With 1 in 5 children falling behind during the 7-16 month interval, mostly a result of missed opportunities, providers should focus on this time interval to deliver all recommended vaccinations that are due.