1. 2011 National Immunization Conference
Two dose varicella vaccination coverage estimates from Immunization Information System (IIS) Sentinel Sites, 2010
Adriana S. Lopez, MHS
CDC/NCIRD/DVD/EB
2011 National Immunization Conference
Washington, DC
March 29, 2011
National Center for Immunization and Respiratory Diseases
Division of Viral Diseases, Epidemiology Branch, Herpes Virus Team

2. Background
June 2006:
Advisory Committee on Immunization Practices (ACIP) recommended routine 2-dose varicella vaccination program for children
First dose: months
Second dose: 4-6 years
Mechanism to measure national 2-dose varicella vaccination coverage currently not available
One dose coverage measured for children months of age using the National Immunization Survey
Currently, we do not have a mechanism to measure national 2-dose varicella vaccination coverage among the age group recommended to receive the 2nd dose.
Unlike for 1-dose coverage, where the National Immunization Survey provides estimates for children months of age.

3. Objective
To estimate two-dose varicella vaccination coverage in children 4-6 years of age,
To determine the age at receipt of first and second dose, and
To determine the frequency of co-administration with MMR vaccine
The objectives of our study were to. . .

4. Immunization Information Systems (IIS) Sentinel Site Project
IIS Sentinel Site Project purpose
Improving quality of IIS data for immunization program assessment
Inclusion criteria for Sentinel Site Project
>85% children <19 years participating in the IIS
>85% of provider sites participating in the IIS
>70% of doses administered reported 0-30 days after administration
8 sites funded
Subsets of AZ, CO, MI, MN, OR, and WI
All of ND and NYC
Covers 6.4 million children <19 years
Sites with 2-dose varicella vaccine school entry requirements: CO, MI, MN, ND, WI
Data for our study was collected from the Immunization Information Systems or IIS sentinel site project.
The purpose of this project is to improve quality of the IIS data for immunization program assessment.
To be included in the sentinel site project, more than 85% of children <19 yrs of age must participate in the IIS, more than 85% of provider sites must participate in the IIS, and more than 70% of doses administered must be reported within 30 days of administration.
8 sites were funded for the cycle. These included subsets of AZ, CO, MI, MN, OR, and WI, all of ND, and all of NYC, covering an estimated 6.4 million children <19 years of age.
Of these sentinel sites, CO, MI, MN, ND, and WI require 2 doses of varicella vaccine for school entry. The remaining sites have 1-dose varicella entry requirements.

5. Varicella Vaccination Coverage: Methods
From January 1, 2006 through June 30, each IIS sentinel site reported # varicella and MMR vaccine recipients 12 months to 18 years of age
Analysis was restricted to children aged 4-6 years during the entire study period
Valid varicella vaccine doses:
First dose: administered on or after 1st birthday minus 4 day grace period
Second dose: administered at least 24 days after 1st dose
Denominators for coverage estimates:
Children in IIS : those with demographic record in IIS with or without varicella disease history
2009 population census data
To measure varicella vaccination coverage, we looked at the number of varicella and MMR vaccine recipients among children 12 months to 18 years of age reported from the sentinel sites from January 2006 through June 2010.
There was no “aging-in” or “aging-out” of the study period so for the analysis, we looked at those kids who were in the year age group during the entire study period. This ensures that all of the kids in the birth cohort had equal opportunity for vaccination during the period of coverage.
Valid vaccine doses were defined as follows:
The first dose could be administered on or after the 1st birthday minus a 4-day grace period
The second dose could be administered at least 24 days after the 1st dose
For the denominators for coverage estimates, we used 2 different sources.
First we used children with a demographic record in the IIS with or without varicella disease history
Next we used the 2009 population census data from the sentinel sites as a comparison

6. Varicella Vaccination Coverage: Calculations
Two calculations:
IIS denominator : Total # children with 1 or 2 valid doses varicella vaccine
estimates Total # children in IIS aged 4-6 years without history of varicella disease
Census denominator: Total # children with 1 or 2 valid doses varicella vaccine
estimates Total # children aged 4-6 years in population
The following calculations were used to determine 1 and 2 dose varicella vaccination coverage among the children in the 4-6 yr age group during our study period
For coverage estimates using IIS denominator data, we took the total # of children with 1 or 2 valid doses of varicella vaccine and divided that by the total # of children in the IIS aged 4-6 yrs without history of varicella disease
For estimates using the census denominator data, we took the total # of children with 1 or 2 valid doses of varicella vaccine and divided that by the total # of children aged 4-6 years in the population

7. Varicella vaccination coverage
Varicella vaccination coverage* among 4-6 year old children, January 2006 through June 2010
Overall 1-dose coverage: 81.7%
Overall 2-dose coverage: 56.4%
Overall varicella vaccination coverage estimates among 4-6 yr old children from January 2006-June 2010 was 81.7% for 1 dose and 56.4% for 2 doses. These calculations were based on using the IIS children as the denominator.
*Children in IIS Sentinel Sites used as denominator

8. Varicella Vaccination coverage
Varicella Vaccination coverage* among children aged 4 to 6 years, by sentinel site, January 2006 through June 2010
The next few slides will also present varicella vaccination coverage as estimated using the IIS sentinel site denominator data. This first slide shows 1-dose varicella vaccination coverage among the 4-6 yr age group. It ranges from 62% in NYC to 93% in CO and is 82% overall.
*Children in IIS Sentinel Sites used as denominator

9. Varicella Vaccination coverage
Varicella Vaccination coverage* among children aged 4 to 6 years, by sentinel site, January 2006 through June 2010
This slide adds 2-dose coverage by site and overall. As you can see, two-dose coverage is lower than 1-dose coverage in all sites, ranging from 32% in NYC to 67% in CO and 56% overall.
In most of the sites with 2-dose school entry requirements, CO, MI, ND, and WI, 2 dose varicella vaccination coverage was >60%.
*Children in IIS Sentinel Sites used as denominator

10. Two dose Varicella and MMR vaccination coverage
Two dose Varicella and MMR vaccination coverage* among children aged 4 to 6 years, by sentinel site, January 2006 through June 2010
Next, we looked at a comparison of the 2nd dose for varicella vs 2nd dose for MMR since they are both recommended to be administered at 4-6 yrs of age. We found that 2-dose varicella vaccination coverage lags behind 2-dose MMR coverage in all sites.
Overall, 2-dose MMR coverage was 77.8% vs 56.4% for 2-dose varicella coverage.
*Children in IIS Sentinel Sites used as denominator

11. How do coverage estimates using IIS data compare to other estimates?
So, how do the coverage estimates using IIS data compare to other estimates?

12. One dose varicella vaccination coverage among 19-35 month olds, IIS, census, and NIS estimates, 2008
First, we looked at a comparison of 1 dose varicella vaccination coverage using IIS denominator data (using data from ), using census population data from 2009 as the denominator, and the National Immunization Survey (2008 estimates). In general, coverage calculated using the census denominator data provided estimates closer to what is seen with the NIS. However, it remains to be seen which denominators would be best to use for varicella vaccination coverage estimates.
Some of the following reasons could explain the differences between the IIS and NIS estimates:
NIS counts all doses whereas IIS counts only valid doses (as defined by query)
IIS are challenged to adjust for mobility of children out of their jurisdictions. May result in higher denominators than what is used for NIS/census and this can also result in incomplete records in the numerator, both of which result in underestimated coverage
NIS does not take into account varicella disease history
Not all providers participate in IIS even though sentinel sites have high participation and those that do participate may not submit all vaccination data
Most sentinel sites include only subsets of entire state
* Vaccines administered on or before 12/31/2008

13. Comparison of 2nd dose varicella vaccination coverage among children aged 4 to 6 years using IIS and census population denominators, January 2006 through June 2010
Next we looked at 2 dose varicella vaccination coverage estimates comparing those calculated by using the IIS denominator data and the census denominator data. The IIS estimates are presented in yellow and the census estimates in white. As seen with the 1-dose estimates, the census estimates are higher for all sites and overall. The overall IIS estimate is 56.4%, while the census estimate is 68.4%.
Based on the differences we found for 2 dose varicella vaccination coverage using IIS versus census data for our denominators, we would be very interested in hearing from those of you in the audience with experience with registries about which denominator you feel reflects vaccination coverage best.

14. Timing of administration of varicella vaccine
We also evaluated timing of the administration of the varicella vaccine among the children in the 4-6 yr age group throughout our study period.

15. Overall 1-dose coverage: 81.7%
Timing of 1st dose of varicella vaccine among 4-6 year olds, who received >1 doses of varicella vaccine, January 2006 through June 2010
The first dose of varicella vaccine is recommended to be administered at months of age. Based on our analysis, we found that 45% of children received their 1st dose at 12 months of age while an average of 67% received their first dose within the recommended timing of months.
Overall 1-dose coverage: 81.7%

16. Timing of 2nd dose varicella vaccine among 4-6 year olds, who received 2 doses of varicella vaccine, January 2006 through June 2010
For the second dose, which again, is recommended to be administered at 4-6 yrs of age, of those who received the 2nd dose, 37% received it at 4 yrs of age and 51% at 5 yrs.
Overall 2-dose coverage: 56.4%

17. Co-administration of Varicella and MMR vaccines among children 4-6 years of age in the IIS sentinel sites, January 2006 through June 2010
Lastly, we looked at frequency of coadministration of Varicella and MMR vaccines since they have the same recommendations for administration.
For the 1st and 2nd doses administered among children 4-6 years of age throughout our study period, a majority of children received both their 1st and 2nd doses of Varicella and MMR vaccines during the same visit but as separate vaccines while only 3% received MMRV for their 1st dose and 22% as their 2nd dose.
Because these children were in the 4-6 yr age group during the entire study period it is possible that MMRV was not available at the time they would have received their first dose, thus explaining the low percentage of MMRV use seen for the 1st dose.
Received both vaccines separately but during same visit
Received both vaccines but at different visits
Received MMRV

18. Limitations
Calculation of coverage estimates challenging using registry data because of issues with denominator
IIS denominators may be inflated because children who move out of the area may not be taken out of the registry
IIS data records history of disease but not complete
Population census denominators include children with history of disease
2-dose varicella vaccination recommendation made in 2006 and likely had slow uptake in earlier years of study period, which may have lowered 2-dose coverage for the study period
Our study was subject to limitations.
Calculation of varicella vaccination coverage estimates is challenging using the registry data because of issues with denominators. With the IIS denominators, they may be inflated because children who move out of the area may not be taken out of the registry. A good example of this are the estimates from NYC that were fairly low (32% for 2 dose coverage). They are subject to denominator problems because they tend to provide care to more children than those that actually reside in the city, thus inflating their denominator.
The IIS data does record history of varicella disease, which is important for varicella vaccination coverage because these would be excluded. However, those data are not necessarily complete.
On the other hand, population census denominator data includes children with history of varicella disease.
Also, the 2 dose recommendation was made in 2006 and uptake was likely slow during the early years of the study period. By using the entire study period, this may have lowered the 2 dose coverage estimates.

19. Conclusions
In the first 4 years of the 2-dose varicella vaccination program, 56.4%-68.4% of children have received 2 doses of varicella vaccine
However, coverage lags behind that for MMR
IIS provides a good source of data to calculate 2-dose varicella vaccination coverage but may underestimate actual coverage as it does for 1-dose
States with 2-dose school entry requirements generally had higher 2-dose varicella vaccination coverage estimates
Most children receiving both varicella and MMR vaccines receive them during the same visit but as separate vaccines
In conclusion,
We estimate that during the first 4 years of the 2-dose varicella vaccination program, from 56% to 68% of children in the 4-6 yr age group received 2 doses of varicella vaccine. Although this is promising, coverage lags behind that for the 2nd dose of MMR.
Although IIS provides a good source of data to calculate 2-dose varicella vaccination coverage, it may underestimate actual coverage as seen with the one dose comparison to NIS and census based estimates.
We found that the states with 2 dose varicella vaccine school entry requirements generally had higher 2 dose varicella vaccination coverage estimates. Thus, adoption of 2-dose school entry requirements for varicella vaccine could increase coverage further.
Lastly, we found that most children received both the varicella and MMR vaccines during the same visit, as recommended, but as separate vaccines.

20. Acknowledgements Sentinel Site Colleagues:
Arizona: Lisa Rasmussen and Patty Gast
Colorado: Diana Herrero and Kimberly Dugger
Michigan: Rachel Potter and Bea Salada
Minnesota: Karen White and Emily Emerson
North Dakota: Keith LoMurray and Molly Sander
New York City: Vikki Papadouka and Michael Hansen
Oregon: Collette Young and Mary Beth Kurilo
Wisconsin: Tom Maerz and Stephanie Schauer
National Center for Immunization and Respiratory Diseases: Karen Cullen, Laura Pabst, Stephanie Bialek
I would like to acknowledge my colleagues from the sentinel site areas and especially my colleagues at CDC, Karen Cullen, Laura Pabst, and Stephanie Bialek.

21. For More Information Contact: Adriana Lopez ALopez@cdc.gov
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The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention

22. One dose Varicella and MMR vaccination coverage among children aged 4 to 6 years, by sentinel site, January 2006 through June 2010

23. MMRV MMRV licensed in 2005 for children 12 months – 12 years
Original recommendation stated that administration of MMRV preferred over MMR + V as 1st or 2nd dose
In 2008, studies identified risk of febrile seizures among children months following receipt of MMRV and recommendation changed to express no preference for MMRV
In June 2009, ACIP updated recommendation after examining all data
1st dose among children mo, MMR + V or MMRV may be given if no family history of seizures but CDC recommends MMR + V
2nd dose or 1st dose in children ≥48 months, MMRV is recommended
Since July 2007, supplies of MMRV have been unavailable due to manufacturing constraints

24. IIS Sentinel Sites Profiles
Area
# of Children <6 yrs old enrolled in IIS and living in sentinel site area
% children <19 years old in population with ≥2 doses in IIS
% of enrolled provider sites
% vaccinations recorded in the IIS within 30 days AZ
Seven counties in northern AZ
85,531
87%
99%
91% CO
14 counties in southwestern CO
13,294
90%
98% MI
81/83 counties in state
518,901
100% MN
Hennepin County (Minneapolis)
107,089
86%
88%
NYC
Manhattan, Bronx, Brooklyn, Staten Island, Queens
899,328
95% ND
Entire state
56,713
97% OR
Washington and Multnomah counties (greater Portland)
94,081
94%
89% WI
5 counties in southern WI (includes Madison)
95,288
This slide just demonstrates the diversity among the sites and includes data from their Quarter quarterly vaccination reports and 2009 mid-year progress reports.
They are not nationally representative and may not be entirely representative of their state.
The eight participating grantees include Arizona, Colorado, Michigan, Minnesota, New York City, North Dakota, Oregon, and Wisconsin.
Although New York City and North Dakota use their entire geographic area for analysis, grantees like Oregon limit their analysis to the greater Portland area and Arizona focuses on the northern part of the state. The smallest site in CO has just over 13,000 children <6 years of age in their 14-county region compared to our most populous site of NYC with almost 900,000 children <6 years of age enrolled in the IIS.
Sites have very timely data with 88% or more of vaccination records processed and entered into the IIS within 30 days.