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The need for surveillance of delay in age-appropriate immunization
Kevin J Dombkowski1, Paula M Lantz, Gary L Freed
1Child Health Evaluation and Research Unit, Division of General Pediatrics, University of Michigan, Ann Arbor 48109-0456, USA. kjd@med.umich.edu
Insights
Many children are up-to-date on vaccinations but received them late. This means current measures may underestimate underimmunization. Age-appropriate vaccination tracking is crucial for public health.
Area of Science:
- Pediatric Health
- Immunization Surveillance
- Public Health Policy
Background:
- National vaccination assessments often focus on up-to-date status, disregarding the timing of dose administration.
- This study utilizes data from the National Health Interview Survey (NHIS) conducted in 2000-2001.
Purpose of the Study:
- To evaluate age-appropriate vaccination status in children aged 25 to 72 months.
- To compare up-to-date vaccination status with age-appropriate vaccination timing.
- To identify potential underestimation of underimmunization by current surveillance methods.
Main Methods:
- Retrospective analysis of pooled NHIS Immunization Supplement data from 1992-1996 for children aged 25-72 months.
- Assessment of vaccination delay in months relative to age-appropriate standards.
- Evaluation of up-to-date and age-appropriate status for DTP4, Polio3, MMR1, and the 4:3:1 series based on written records.
Main Results:
- 80% of children achieved the 4:3:1 vaccination series, but 48% experienced delays.
- While 85% were up-to-date for DTP4, only 46% received it at the appropriate age.
- Significant discrepancies were observed for Polio3 (64% age-appropriate) and MMR1 (58% age-appropriate).
- Age-appropriate DTP4 vaccination improved by 17% from 1992-1996, while up-to-date status increased by only 6%.
Conclusions:
- Up-to-date vaccination status often masks considerable delays in age-appropriate immunization.
- Relying solely on up-to-date status can underestimate the true extent of underimmunization in populations.
- National surveillance must incorporate age-appropriate vaccination metrics to identify at-risk groups and trends.
Background:
Vaccination status is assessed nationally in terms of up-to-date status without regard to the age at which recommended doses were actually received. Our study was conducted in 2000-2001 using the most current National Health Interview Survey (NHIS) public use files available.
Methods:
Retrospective analysis to determine up-to-date and age-appropriate vaccination status for children aged 25 to 72 months. Five years of pooled data (1992-1996) were obtained from the NHIS Immunization Supplement for children aged 25 to 72 months with immunization data based on written records. The outcome measures used were months of vaccination delay relative to age-appropriate vaccination standard as well as up-to-date vaccination status for the fourth diphtheria-tetanus-pertussis (DTP 4), Polio3, the first measles-mumps-rubella (MMR1) doses, and the 4:3:1 series.
Results:
Of the 9223 eligible children, 80% were up-to-date for the 4:3:1 vaccination series, but 48% had experienced delays relative to age-appropriate standards. For the DTP4 dose, 85% were up-to-date, although only 46% had received this dose at the appropriate age. Similarly, 90% of children were up-to-date with their Polio3 dose, with 64% receiving this dose at the appropriate age; 96% were up-to-date for the MMR1, and 58% received this dose at the appropriate age. Age-appropriate DTP4 vaccination increased by 17 percentage points from 1992 to 1996, whereas up-to-date DTP4 status increased by only 6% during the same period.
Conclusions:
Children with up-to-date vaccination status often experienced considerable delay relative to age-appropriate vaccination standards. Consequently, vaccination status measures based solely on up-to-date status tend to understate the degree of underimmunization in a population. National surveillance of age-appropriate vaccination is necessary to identify subpopulations with the greatest prevalence of vaccination delay and to reveal underlying trends that may not be evident through assessments of up-to-date status.