Population-based incidence of herpes zoster after introduction of a publicly funded varicella vaccination program☆
Highlights
► We assessed the impact of childhood varicella vaccination on herpes zoster. ► Zoster incidence decreased 29% for children aged 0–9 and changed minimally for others. ► Zoster hospitalizations declined by 53%, while outpatient visits declined by 9%. ► Overall, varicella vaccination did not increase rates of herpes zoster.
Introduction
Varicella zoster virus (VZV) infection results in chicken-pox (varicella). After an initial infection, VZV remains dormant in the dorsal and trigeminal ganglion cells of those infected and may reactivate to cause shingles (herpes zoster). Zoster typically presents as a unilateral, painful vesicular rash with a dermatomal distribution. Zoster infection may lead to postherpetic neuralgia, a chronic and debilitating complication of the disease.
Zoster causes substantial morbidity in older populations and is anticipated to be a growing concern given Canada's aging population. A zoster vaccine that decreases the incidence of both zoster and post-herpetic neuralgia was approved and made available in Canada in late 2009 for adults 60 years or older [1], [2].
Varicella vaccination decreases the incidence of varicella and varicella-related outcomes [3], [4], [5], [6], [7], [8]. Exposure to varicella is thought to boost immunity against reactivation of varicella as zoster [9]. Modeling studies predict that a reduction in varicella cases will consequently lead to an initial increase in zoster, followed by an eventual decline [10], [11], [12]. There has been great interest in monitoring zoster incidence following introduction of the varicella vaccine, with previous studies finding conflicting results [13], [14], [15], [16], [17]. In the province of Ontario, varicella vaccines were made available for private purchase in 1999, and have been funded by a governmental program since 2005 for susceptible, unimmunized children ages 12–15 months and 4–6 years. A previous study indicated significant declines in rates of medically attended varicella in Ontario following private and publicly funded availability [8].
Building on the inconclusive evidence of the early effects of varicella vaccine on zoster incidence, we examined population-based, health administrative databases of hospitalizations and outpatient visits for over 12 million people in Ontario, Canada over a span of 18 years. We sought to assess the early impact of routine childhood varicella vaccination on zoster incidence and healthcare use in the population, and to establish baseline zoster rates in the elderly prior to mass adoption of zoster vaccine.
Section snippets
Methods
We studied rates of zoster cases requiring healthcare use in the Ontario population (N = 13.2 million in 2010) from April 1992 to March 2010 (fiscal year (FY) 1992–2009). Using encrypted health card numbers as unique identifiers, records of hospitalizations and visits to physician offices and emergency departments were linked across databases. Ethics approval was obtained from the Sunnybrook Health Sciences Centre Research Ethics Board in Toronto, Canada.
Results
Over an 18-year period, 686,763 individuals in Ontario sought medical attention for zoster. This included 14,240 hospitalizations (6.7 per 100,000), including 6751 admissions with zoster as the primary diagnosis (3.2 per 100,000). Additionally, there were 1,120,063 total outpatient visits (527 per 100,000). The overall crude annual incidence rate of medically attended zoster was 323 per 100,000 (Table 1). Incidence rates, hospitalization rates, and rates of outpatient visits for zoster were
Discussion
Five years after the introduction of a publicly funded, routine childhood varicella vaccination program in Ontario, and over 12 years after approval of varicella vaccines in Canada, incidence rates of medically attended herpes zoster changed minimally for the Ontario population and decreased moderately for children 9 years and younger, the age group targeted for varicella vaccination. Public funding of varicella vaccination for children aged 15 months has prevented varicella (and subsequent
Acknowledgements
Contributors: Peter Tanuseputro contributed substantially to conception and design, and analysis and interpretation of data; drafted the article and revised the article critically for important intellectual content; and gave final approval of the version to be published. Brandon Zagorski contributed substantially to conception and design, acquisition of data, and analysis and interpretation of data; revised the article critically for important intellectual content; and gave final approval of
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The opinions, results and conclusions reported in this paper are those of the authors and are independent from the funding sources. No endorsement by ICES or the Ontario MOHLTC is intended or should be inferred.