Date of Award

January 2014

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

James L. Hadler

Abstract

Background: A vaccine for primary varicella (VZV) was licensed and recommended for use in children as a single dose in 1996, and as two doses in 2006. A vaccine for herpes zoster (HZ) was licensed and recommended for use in adults ≥60 years in 2006. Both vaccines have the potential to modify the epidemiology of VZV and HZ. Rates of hospitalization due to VZV and HZ were examined in the post-vaccine era to characterize the epidemiology of severe disease and to assess the possible impact of vaccination on the incidence of hospitalization.

Methods: Statewide hospital discharge data in Connecticut were used to identify cases of VZV and HZ from 1994-2012. Trends in hospitalization rates were assessed using Poisson regression models or Mantel-Haenszel chi-square tests.

Results: Primary varicella hospitalization rates declined 82.9% from the pre-vaccine (1994- 1995) to the 1-dose (2001-2005) era (p<0.001). Rates further decreased significantly in the 2- dose era (2010-2012) only among 5 to 9 year olds. HZ hospitalization rates decreased in individuals 0-29 years and 30-39 years by 4.8%/year and 6.1%/year, respectively, from 2001- 2012. Individuals <15 years experienced the largest decline, at 19.4%/year from 2001- 2012. Among individuals ≥60 years, hospitalization rates increased by 5.1%/year from 2001- 2006 but then decreased by 4.2%/year from 2007-2012.

Conclusions: Introduction of the varicella vaccine appears to have had an impact on both varicella and HZ hospitalizations. Varicella hospitalization rates decreased across all age groups following vaccine introduction, though the main impact occurred during the 1-dose era. HZ hospitalization rates decreased among individuals <15 years from 2001-2012, providing early evidence of varicella vaccine impact. The increase in HZ hospitalization rates among individuals ≥60 years 2001-2006 may be due to decreased varicella virus circulation and lack of immune boosting. However, the reduction in HZ morbidity from 2007-2012 suggests HZ vaccine, despite low usage rates, is offsetting the increase. Increased use of the HZ vaccine in individuals ≥60 years is needed to reduce hospitalization rates first to the levels seen prior to varicella vaccine introduction and then lower. Ongoing surveillance for HZ is needed to monitor anticipated long-term changes in disease epidemiology; hospital discharge data is a feasible method to do so.

Comments

This is an Open Access Thesis.

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