Changes in vaccination coverage estimates among children aged 19–35 months in the United States, 1996–1999

Abstract

Background: Childhood vaccinations have a major impact on the reduction and elimination of many causes of morbidity and mortality among children. Monitoring of annual vaccination coverage levels over time is necessary to characterize undervaccination. Here, coverage estimates for 1996 (1997 for varicella) were compared with those of 1999. Methods: Immunization coverage among children aged 19 to 35 months in 1996 (1997 for varicella) and 1999 for a variety of vaccines and vaccine series were compared using Wald chi-square tests and data from the National Immunization Survey. Results: Record high immunization coverage among children aged 19 to 35 months in the United States has increased by a statistically significant amount between 1996 and 1999 for diphtheria, tetanus, and pertussis; measles, mumps, and rubella; Haemophilus influenzae type b; hepatitis B; and standard series made up of these individual vaccines. Coverage with the vaccine for varicella dramatically increased between 1997 and 1999. However, between 1996 and 1999, coverage with three or more doses of polio vaccine decreased by a small but statistically significant amount. Conclusion: Despite the drop for polio vaccine, coverage remains high. Continued monitoring is required to determine if the drop in polio coverage is a cause for concern.