Herpes Zoster Vaccine

Problem Statement

Chickenpox caused by the varicella-zoster virus (VZV) is an acute contagious viral disease. The VZV virus belongs to the herpesviridae family. There is only one known serotype and humans are the only reservoir (1) The virus is transmitted via aerosols, droplets, or direct contact with the respiratory secretions of infected individuals. While the infection usually has a mild course in children, it follows a more severe course in adults and older patients, who also have a greater risk of developing life-threatening complications (1). Individuals at the highest risk of severe infection include neonates, immunocompromised persons, adults, and smokers (2). Varicella is the leading vaccine-preventable cause of death in children (3). The rate of hospitalization in adults is 900% higher than in children. Adults account for an incidence of only 5%, these 5% cases account for 35% of the deaths. Thus, the case fatality rate is 40 times higher in adults than in children (1)

Complications of varicella zoster infection include superimposed bacterial infection, thrombocytopenia, hepatitis, pneumonia, encephalitis, or death (2).

The virus that causes chickenpox remains dormant in the dorsal root ganglia, and upon reactivation, the virus causes herpes zoster (shingles).

All these factors warrant large-scale immunization of the population against the virus.

Mechanism of Action

The varicella-zoster vaccine contains the live attenuated strain of varicella-zoster virus the Oka Strain. The strain is modified via cell propagation in different cell cultures. The vaccine induces humoral and cellular immunity, the humoral component is mediated via the generation of IgG antibodies, whereas the cell-mediated immunity is through the activation of CD4+ T-helper cells and CD8+ T-lymphocyte cells (4).

Indications

While some countries have recommended universal varicella vaccination, it is of utmost importance to immunize the following groups of people: (6)

• Close contact with people at high risk for disease (caregivers of immunocompromised people)
• High risk of exposure:
  • Teachers of young children
  • Child care employees
  • Adults with children in the household
  • Correctional institution staff and residents
  • College students
  • Military recruits
  • International traveller’s
  • Nonpregnant females of reproductive age
• Immigrants and refugees

Absolute Contraindications (6,7,8,9,)

• Pregnancy or trying to become pregnant
• Severe Allergic reaction to previous dose or component of vaccine
• Severe immunosuppression due to any cause
• Active tuberculosis, not treated
• Long-term glucocorticoid therapy

Relative Contraindications:

• For recipients of blood products containing antibodies or passive immunization, the vaccine can be administered 6 months after transfusion, if the blood product is administered after the vaccination, the second dose should be repeated after 6 months (8)
• Avoid antiviral therapy for 14 days after vaccination (10)
• Avoid salicylates for 6 weeks after vaccination (6)

Schedule

The Centre for Disease Control (CDC) recommends the following for the Varicella Zoster Vaccine:

• For children = 12 months 0.5 ml of reconstituted vial via intramuscular or subcutaneous route
• A total of 2 doses must be administered, first dose at age 12-15 months and second dose at 4-6 years of age
• The second dose may be administered earlier if = 3 months have passed since the first dose
• The minimum duration between the doses must be at least 4 weeks

World Health Organisation (WHO) recommends the following for the Measles Mumps Rubella Varicella Vaccine (MMRV):

• A total of 2 doses must be administered, first dose at age 9 months
• The second dose should be administered 6 weeks to 3 months after the first dose for children < 13 years
• The second dose may be administered after 4 to 6 weeks for children > 13 years and adults
• The minimum duration between the doses must be at least 4 weeks

Side Effects

• Local: pain, redness, or tenderness at the injection site
• Localized rash at the site of injection lesion
• Generalized rash within a month of vaccination
• Temperature > 102°F in 15% of children under 13 years of age
• Rarely, disseminated varicella, meningitis, or encephalitis from vaccine virus