A comparison of varicella vaccination coverage estimates: what happens to coverage estimates when children with a history of varicella disease are considered "vaccinated"?

Learning Objectives for this Presentation:
By the end of the presentation, participants will be able to describe the effect of including history of varicella disease in the calculation of varicella vaccination coverage estimates at national and state levels.

Background:
Varicella vaccination coverage is based on 1+ doses of varicella vaccine at or after the first birthday. The calculation of varicella vaccination coverage does not routinely take history of varicella disease into consideration. Children with a history of varicella disease may not have received the varicella vaccine and would be considered unvaccinated.

Objectives:
Describe the change at national and state levels in varicella vaccination coverage estimates among children aged 19-35 months when history of varicella disease is taken into consideration.

Methods:
The 2006 National Immunization Survey (NIS) data were used to calculate coverage estimates at national and state levels. Varicella vaccination coverage estimates and 95% confidence intervals were calculated based on receipt of 1+ doses of varicella vaccine and in combination with a history of varicella disease. T tests were conducted to test for differences between estimates.

Results:
At the national level, varicella vaccination coverage that includes history of varicella disease differed by 1% from varicella vaccination coverage that did not include history of varicella disease (90.3%, 89.7-91.0 95%CI compared to 89.3%, 88.6-90.0 95%CI, respectively). State coverage estimates increased by up to 3.8%. Coverage increased above 90% in two states (Michigan and North Dakota) when history of varicella disease was considered, but the increases were not statistically significant.

Conclusions:
Using a measure of varicella vaccination that includes both vaccination and history of varicella disease does increase national and state level coverage estimates for varicella vaccine and contributes to the status of having already reached the Healthy People 2010 objective of 90% coverage at the national level compared to a measure that includes only vaccination.