Varicella Vaccine Effectiveness in Preventing Community Transmission in the 2-Dose Era
Published Date:Mar 14 2016
Pubmed Central ID:PMC4887293
Funding:CC999999/Intramural CDC HHS/United States
We examined overall and incremental effectiveness of 2-dose varicella vaccination in preventing community transmission of varicella among children aged 4–18 years in two active surveillance sites. One-dose varicella vaccine effectiveness (VE) was examined in those aged 1–18 years.
From May 2009 through June 2011, varicella cases identified during active surveillance in Antelope Valley, CA and Philadelphia, PA were enrolled into a matched case-control study. Matched controls ±2 years of the incident case's age were selected from immunization registries. A standardized questionnaire was administered to participants' parents, and varicella vaccination history was obtained from healthcare provider, immunization registry, or parent records. We used conditional logistic regression to estimate varicella VE against clinically-diagnosed and laboratory-confirmed varicella.
One hundred twenty-five clinically-diagnosed varicella cases and 408 matched controls were enrolled. Twenty-nine cases were laboratory-confirmed. One-dose VE (1-dose vs. unvaccinated) was 75.6% [95% confidence interval (CI): 38.7–90.3%] in preventing any clinically-diagnosed varicella and 78.1% (95% CI: 12.7–94.5%) against moderate/severe, clinically-diagnosed disease (≥50 lesions). Among subjects aged ≥4 years, 2-dose VE (2-dose vs. unvaccinated) was 93.6% (95% CI: 75.6–98.3%) against any varicella and 97.9% (95% CI: 83.0–99.7%) against moderate/severe varicella. Incremental effectiveness (2-dose vs. 1-dose) was 87.5% against clinically-diagnosed varicella and 97.3% against laboratory-confirmed varicella. Compared with 1-dose breakthrough cases, 2-dose cases had shorter duration of rash (P=0.01) and were 80% less likely to develop vesicular rashes (P=0.01).
Two-dose varicella vaccination offered improved protection against varicella from community transmission among school-aged children compared with 1-dose vaccination.
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