Background: Varicella vaccine was recommended for children in 1995 and herpes zoster (HZ) vaccine was recommended for adults 60 years and older in 2008. We analyzed trends in HZ incidence from 1993-2013 to investigate the impact of these vaccination programs.
Methods: Medical claims data from MarketScan« Databases were obtained for 1993-2013, extending our past analysis (1993-2006). We identified HZ based on first outpatient service with an HZ ICD-9 code (053.xx) and calculated unadjusted incidence.
Results: As we reported in the past , HZ incidence increased in all age strata (Fig. 1) from 1993, before availability of varicella vaccine, through 2006 (p<0.0001). However, since then, incidence has plateaued in adults aged ≥55 years. Incidence also plateaued in young adults aged 18-34 years, with a decline in children aged ≤17 years (Fig. 2).
Conclusion: We cannot explain the plateauing of HZ incidence in adults, just as we are unable to explain the preceding increase. It cannot be attributed to HZ vaccine, since national HZ vaccine uptake among persons 60 and older was <2% in 2007, increasing to just 16% by 2011. Nonetheless, these recent data provide additional evidence that varicella vaccination is not responsible for increasing rates of HZ in the U.S. áRegarding pediatric HZ, we believe declining incidence can be explained by varicella vaccination: >90% of children aged 10-17 years were infected with varicella zoster virus (VZV) prior to the varicella vaccine era and experienced the same age-specific increases observed in VZV-infected adults. Over time, successive birth cohorts were progressively more likely to receive varicella vaccine, comprised of attenuated VZV that is much less likely to reactivate and cause HZ, and they were also less likely to be exposed to and infected with wild type VZV. These developments have resulted in the observed HZ declines.
M. Gambhir, None