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

Varicella Vaccination: Indiana School Requirements 2009-2010 School Year : 1 Dose K – 12th grades 2010-2011 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%

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

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

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

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.

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

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

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

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

School Data N = 16 Median Age = 10 years

Disease Severity N = 142

Vaccination Status N = 146

Severity by Vaccination History N = 141

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

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

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

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

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

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

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

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

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

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