Herpes Zoster Following Varicella Vaccination in Children

Varicella-zoster virus (VZV) causes varicella as a primary infection. It is a highly contagious disease characterized by a widespread papulovesicular eruption with fever and malaise.^1,2 After the primary infection, the virus remains latent within the sensory dorsal root ganglia and can reactivate as herpes zoster (HZ).^1-5 Herpes zoster is characterized by unilateral radicular pain and a vesicular rash in a dermatomal pattern.^1,2 It is most common in adults, especially elderly and immunocompromised patients, but rarely occurs in children. Herpes zoster is most often seen in individuals previously infected with VZV, but it also has occurred in individuals without known varicella infection,^1-17 possibly because these individuals had a prior subclinical VZV infection.

A live attenuated VZV vaccine was created after isolation of the virus from a child in Japan.² Since the introduction of the vaccine in 1995 in the United States, the incidence of VZV and HZ has declined.⁵ Herpes zoster rates after vaccination vary from 14 to 19 per 100,000 individuals.^3,5 Breakthrough disease with the wild-type strain does occur in vaccinated children, but vaccine-strain HZ also has been reported.^1-5 The risk for HZ caused by reactivated VZV vaccine in healthy children is unknown. We present a case of HZ in an otherwise healthy 19-month-old boy with no known varicella exposure who received the VZV vaccine at 13 months of age.

Case Report

An otherwise healthy 19-month-old boy presented to the dermatology clinic with a rash that began 2 days prior on the right groin and spread to the right leg. The patient’s mother denied that the child had been febrile and noted that the rash did not appear to bother him in any way. The patient was up-to-date on his vaccinations and received the first dose of the varicella series 6 months prior to presentation. He had no personal history of varicella, no exposure to sick contacts with varicella, and no known exposure to the virus. He was otherwise completely healthy with no signs or symptoms of immunocompromise.

Physical examination revealed grouped vesicles on an erythematous base on the right thigh, right sacrum, and lower abdomen that did not cross the midline (Figure). There were no other pertinent physical examination findings. The eruption was most consistent with HZ but concern remained for herpes simplex virus (HSV) or impetigo. A bacterial culture and polymerase chain reaction assay for VZV and HSV from skin swabs was ordered. The patient was prescribed acyclovir 20 mg/kg every 6 hours for 5 days. Laboratory testing revealed a positive result for VZV on polymerase chain reaction and a negative result for HSV. The majority of the patient’s lesions had crusted after 2 days of treatment with acyclovir, and the rash had nearly resolved 1 week after presentation. Subsequent evaluation with a complete blood cell count with differential and basic metabolic profile was normal. Levels of IgG, IgA, and IgM also were normal; IgE was slightly elevated.

Grouped vesicles on an erythematous base with secondary crusting along the L4 dermatome of the right thigh on day 2 of the eruption (A) and right sacrum on day 3 of the eruption (B).

Comment

Herpes zoster in children is an uncommon clinical entity. Most children with HZ are immunocompromised, have a history of varicella, or were exposed to varicella during gestation.⁸ With the introduction of the live VZV vaccine, the incidence of HZ has declined, but reactivation of the live vaccine leading to HZ infection is possible. The vaccine is 90% effective, and breakthrough varicella has been reported in 15% to 20% of vaccinated patients.^1-17 The cause of HZ in vaccinated children is unclear due to the potential for either wild-type or vaccine-strain VZV to induce HZ.

Twenty-two cases of HZ in healthy children after vaccination were identified with a PubMed search of articles indexed for MEDLINE using the search terms herpes zoster infection after vaccination and herpes zoster infection AND immunocompetent AND vaccination in separate searches for all English-language studies (Table). The search was limited to immunocompetent children and adolescents who were 18 years or younger with no history of varicella or exposure to varicella during gestation.

The mean age for HZ infection was 5.3 years. The average time between vaccination and HZ infection was 3.3 years. There was a spread of dermatomal patterns with cases in the first division of the trigeminal nerve, cervical, thoracic, lumbar, and sacral distributions. Of the 22 cases of HZ we reviewed, 16 underwent genotype testing to determine the source of the infection. The Oka vaccine strain virus was identified in 8 (50%) cases, while wild-type virus was found in 8 (50%) cases.^{1,2,4,5,7,8,10,11,13,14,16} Twelve cases were treated with acyclovir.^{2,3,5,6,9-12,14-17} The method of delivery, either oral or intravenous, and the length of treatment depended on the severity of the disease. Patients with meningoencephalitis and HZ ophthalmicus received intravenous acyclovir more often and also had a longer course of acyclovir compared to those individuals with involvement limited to the skin.

This review found HZ occurs from reactivation of wild-type or Oka vaccine-strain VZV in immunocompetent children.^1-17 It shows that subclinical varicella infection is not the only explanation for HZ in a healthy vaccinated child. It is currently not clear why some healthy children experience HZ from vaccine-strain VZV. When HZ presents in a vaccinated immunocompetent child without a history of varicella infection or exposure, the possibility for vaccine strain–induced HZ should be considered.