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

Background: Childhood vaccinations have a major impact on the reduction and elimination of many causes of morbidity and mortality among children. Moni toring of annual vaccination coverage levels over time is necessary to char acterize undervaccination. Here, coverage estimates for 1996 (1997 for vari cella) were compared sith 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 rising Wald chi-square tests and data from the National Immun ization Survey. Results: Record high immunization coverage among children aged 19 to 35 mon ths in the United States has increased by a statistically significant amoun t between 1996 and 1999 for diphtheria, tetanus, and pertussis; measles, mu mps, 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 19 96 and 1999, coverage with three or more doses of polio vaccine decreased b y a small but statistically significant amount. Conclusion: Despite the drop for polio vaccine, coverage remains high. Cont inued monitoring is required to determine if the drop in polio coverage is a cause for concern.