1. Varicella Vaccine Efficacy Estimates
Dana A. Hazen, RN, MPH
Indiana State Department of Health
Layla Baker, MD, MPH
Regenstrief Institute

2. Varicella Vaccination: Indiana
School Requirements
School Year : 1 Dose K – 12th grades
School Year:
2 Dose K; 6-12th grade
1 Dose 1st – 5th grade
Current coverage in Indiana (estimates)
1 dose (NHIS) 85.7%
2 dose (CHIRP) 70%

3. Varicella Surveillance: Indiana
Outbreaks reportable for 10+ years
Individual cases reportable as of 12/12/2008 by physicians, hospitals and laboratories through passive surveillance

4. Purpose
Describe varicella outbreak activity in Indiana from 12/1/09 – 12/1/10
Report vaccine efficacy of 2-dose series in outbreaks

5. Case Definition: Chickenpox
Acute onset of generalized maculopapular or vesicular rash illness in absence of other clinical diagnosis occurring <7 days or >42 days post vaccination AND
Epidemiological Link to Other Case OR
Positive Varicella Zoster Virus DNA detection by PCR or isolation of varicella virus from specimen through culture with clinical diagnosis of chicken pox

6. Outbreak Definition: Chickenpox
Age 12 and Under: 5 or more cases* that are linked by person and place within 1 incubation period
Age 13 and Up: 3 or more cases* that are linked by person and place within 1 incubation period.
Onset dates between 12/1/09 – 12/1/10.
*Cases reported by school nurses, parents or physician offices.

7. Data Collection: Laboratory Testing
Specimens collected by nurse at school, physician’s office or local health department
2 specimens for each case
Scraping of skin lesions
Varicella Zoster Virus (VZV) by rapid PCR
Specimen submitted to CDC VZV Lab for viral strain typing

8. Varicella School Outbreak Summary Form
Vaccination Coverage Rates at the Onset of the First Case
Number of Students:
Vaccinated Once
Vaccinated Twice
Disease History
Vaccine and Disease History
No Vaccination or Disease History
Unknown Vaccine History
Number of Student cases
Number of Staff cases

10. Vaccine Efficacy Calculations
Vaccination Coverage Rate (%):
Number of children who have received x doses varicella vaccine X 100
Number of children eligible to receive x doses varicella vaccine
Vaccine Efficacy (VE) %:
Attack Rate unvaccinated – Attack Rate vaccinated X 100
Attack Rate unvaccinated
*Cases with known disease history or unknown vaccination status were excluded from the calculations

11. Results 12/1/09– 12/1/10: 388 cases reported in Indiana 11 outbreaks
Involved 16 Schools
Range: 5-36 cases
3 confirmed wild-type virus
147 cases linked to outbreaks
No hospitalizations or deaths
4 confirmed cases
11 diagnosed by HCP

12. School Data N = 16
Median Age = 10 years

13. Disease Severity N = 142

14. Vaccination Status N = 146

15. Severity by Vaccination History N = 141

16. School-Based Outbreaks
NUMBER OUTBREAKS
CASES
SCHOOLS
11 Outbreaks
147 Cases
16 Schools

17. School-Based Outbreaks
NUMBER OUTBREAKS
CASES
SCHOOLS
11 Outbreaks
147 Cases
16 Schools
School-side Vaccination Coverage Rates Available
School-side Vaccination Coverage Rates Available
5 Outbreaks*
77 Cases
6 Schools
* One outbreak missing data for 1 of the schools

18. School-Based Outbreaks
NUMBER OUTBREAKS
CASES
SCHOOLS
11 Outbreaks
147 Cases
16 Schools
School-side Vaccination Coverage Rates Available
School-side Vaccination Coverage Rates Available
5 Outbreaks
77 cases
6 Schools
Excludes staff and siblings of students
73 Cases*
*There were 66 cases with known Vax Status and No History of Disease

19. Vaccination Coverage Rates
Overall Vaccine Coverage Rate = 93.8 %
Vaccine Coverage Rate for One Dose Vaccine = 65.3 %
Vaccine Coverage Rate for Two Doses Vaccine = 28.4 %
Vaccination Coverage Rates
Outbreak
Date(s)
Vaccine Coverage Rate
Number of cases
Total
12/01/09 – 12/01/10
93.8% 73 1
01/29/10 – 03/14/10
100 % 7 2
01/18/10 – 03/31/10
99. 1% 21 3
11/11/10 – 11/27/10
64.2 % 4
08/30/10 – 09/18/10
87.3% 10 5
12/04/09 – 03/08/10
99.4 % 28

20. Attack Rates Vaccination Status Attack Rate Vaccinated 2.0 %
1 Dose Vaccine
2.8 %
2 Dose Vaccine
0.38%
Unvaccinated
7.7%

21. Vaccine Efficacy Vaccination Status Estimate Overall 73.1 %
1 Dose Vaccine
63.5 %
2 Dose Vaccine
94.9 %

22. Limited lab Confirmations Misclassification of cases
Study Limitations
No Estimate exposure
Low Case Counts
Limited lab Confirmations
Misclassification of cases
No analysis of age at vaccination

23. Conclusion
Vaccine efficacy estimates are similar to those reported by other studies
Results demonstrate need for increased school requirements for the second dose of the vaccine
Consider exclusion during outbreaks for unvaccinated students

24. Acknowledgements
Centers for Disease Control and Prevention
IN School Nurses
IN Public Health Nurses
IN State Dept of Health Field Epidemiologists

25. dhazen@isdh.in.gov lbaker@regenstrief.org
Thank you!