Twenty years of medically-attended pediatric varicella and herpes zoster in Ontario, Canada: A population-based study

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Abstract

Objective To determine if reductions in medically-attended pediatric varicella and herpes zoster occurred in Ontario, Canada, after publicly-funded varicella immunization was implemented in 2004. Methods For fiscal years (FY) 1992-2011, we examined data on varicella and herpes zoster physician office visits, emergency department (ED) visits, hospitalizations (including for varicellaassociated skin and soft tissue infections [SSTI]), and intensive care unit (ICU) admissions, among those aged 18 years. The pre-vaccine, privately-available, and vaccine program eras were FY1992-1998, FY1999-2003, and FY2004-2011, respectively. We used Poisson regressionand Kruskal-Wallis tests (all at the p0.05 level of significance), and compared rates using incidence rate ratios (IRRs) and 95% confidence intervals (CIs). Results Incidence of varicella office visits declined over the study period from a high of 25.1/1,000 in FY1994 to a low of 3.2/1,000 in FY2011. ED visits and hospitalizations followed similar patterns of decreasing rates later in the study period. IRRs comparing the vaccine program versus pre-vaccine eras were 0.29 (95%CI: 0.26-0.32) for office visits, 0.29 (95%CI: 0.21-0.40) for ED visits, and 0.41 (95%CI: 0.10-1.69) for hospitalizations. Annual declines in varicella office visits were 7.7%, 9.1%, 8.4%, and 8.4% per year among children aged 1 year, 1-4 years, 5-11 years, and 12 years, respectively (all p0.001). Age-specific rates of varicellaassociated SSTI declined significantly among children 12 years (p0.001) and rates of ICU admissions decreased significantly for children 1 year (p = 0.02). (p0.001) over the study period. For children aged 5-17 years, herpes zoster office visits decreased whereas ED visits increased (both p0.001) and there was a small, non-significant (p = 0.07), decrease in hospitalizations. Conclusion Medically-attended varicella decreased during the study period, particularly since varicella vaccine was publicly-funded. Results suggest immunization program-related changes in varicella epidemiology, including herd effects, demonstrated by reductions in varicella in program-ineligible age groups. We did not observe a consistent impact on herpes zoster.

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Wormsbecker, A. E., Wang, J., Rosella, L. C., Kwong, J. C., Seo, C. Y., Crowcroft, N. S., & Deeks, S. L. (2015). Twenty years of medically-attended pediatric varicella and herpes zoster in Ontario, Canada: A population-based study. PLoS ONE, 10(7). https://doi.org/10.1371/journal.pone.0129483

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