Learning Objectives for this Presentation:
By the end of the presentation participants will be able to describe the clinical presentation of vaccinated HZ cases by viral strain.

Background:
Herpes zoster (HZ) caused by reactivation of latent varicella zoster virus (VZV) appears to be rare in VZV vaccinees. A severe HZ case in a vaccinated immunocompromised child experiencing reactivation of vaccine strain VZV has been reported; vaccine strain reactivations also have been documented in apparently healthy children.

Objectives:
To describe the VZV viral strains (wild-type versus Oka-Merck vaccine VZV) isolated from HZ cases in vaccinated children and the clinical presentation of vaccinated HZ cases by viral strain.

Methods:
As part of routine surveillance, PDPH has obtained lesion specimens from suspected HZ cases among VZV vaccinees <20 years of age since 2001. The CDC National VZV Laboratory tested specimens for the presence of VZV DNA and discriminated wild-type and Oka-Merck vaccine strain VZV using strain-specific Polymerase Chain Reaction (PCR). PDPH staff interviewed the suspected cases to collect clinical information. We performed descriptive analyses to examine clinical presentation by viral strain for a case series of vaccinated children with HZ.

Results:
Specimens from 13 vaccinated HZ cases <20 years of age were tested using strain-specific PCR. Four vaccinated HZ cases aged 6-11 years were wild-type VZV reactivations, and nine aged 1-9 years were vaccine strain reactivations. One wild-type reactivation and one vaccine strain reactivation reported previous varicella histories. None had immunocomprising conditions. Three-fourths of the wild-type reactivations experienced moderate/severe pain compared to 29% of the vaccine strain reactivations. Complications occurred in two wild-type reactivations with one hospitalization. Household VZV transmission occurred from the hospitalized case.

Conclusions:
Our case series suggests that among healthy vaccinated children, HZ due to reactivations of vaccine strain VZV may be less severe than cases due to wild-type VZV. Further study including testing for viral strain identification is needed.