Abstract
The impact of universal varicella vaccination on herpes zoster (HZ) risk in unvaccinated and vaccinated children, and its long-term influence on HZ epidemiology, remains unknown. We conducted a retrospective cohort study using population-based administrative health data for children born between 1993 and 2018 (n = 924,124). We calculated age-specific cumulative HZ incidence rates by vaccination status for cohorts born before (1993–1999) and after (2000–2018) programme implementation; results were used to calculate relative risk of HZ by age group, vaccination status and vaccine availability period. Annual HZ incidence rates were calculated for 1993–2018. HZ risk was higher among unvaccinated children compared to vaccinated children across age groups; 64% higher before universal vaccination (RR: 0.36, 95% CI: 0.33, 0.39), and 32% higher after universal vaccination (RR: 0.68, 95% CI: 0.64, 0.73). Among unvaccinated children, HZ risk was 60% lower after vaccine programme implementation (RR: 0.40, 95% CI: 0.38, 0.43). Two-dose receipt corresponded with a 41% lower risk of HZ compared to one-dose receipt (RR: 0.59, 95% CI: 0.53, 0.65). Crude annual HZ incidence rates declined 64% after programme implementation, with decreases observed across age groups. Universal varicella vaccination programme implementation corresponds to decreased paediatric HZ incidence across age groups, in both vaccinated and unvaccinated individuals. Results from this study can be used to help inform varicella vaccination programme decision-making in other countries.
Highlights
Herpes zoster (HZ) results from reactivation of latent varicella zoster virus (VZV), introduced through primary varicella infection
Our results demonstrate that the overall HZ incidence rate among vaccinated children was lower in the universal vaccination period than the pre-universal vaccination era, suggesting HZ risk among vaccinated children will decrease as circulating wild-type VZV (wt-VZV) decreases
Paediatric HZ incidence rates in Alberta significantly decreased after implementation of a universal varicella vaccination programme
Summary
Herpes zoster (HZ) results from reactivation of latent varicella zoster virus (VZV), introduced through primary varicella infection. Reactivation of VZV can occur decades after primary infection and is generally associated with a decline in cell-mediated immunity due to aging or immunosuppressive illness/medication. While most common among older adults, HZ does occur in healthy children and adolescents. Prior to varicella vaccination programmes, approximately 9% of HZ cases in Canada occurred in individuals less than 10 years of age [1, 2]. In Alberta, varicella vaccine was available through private purchase in 1999–2001, coverage was less than 5% in 2001 [1], indicating minimal vaccine uptake via private purchase. Varicella vaccine was added to the publicly funded vaccination schedule in July 2001. The publicly funded programme offered universal vaccination
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