Description

Varicella-zoster virus (VZV) is a highly contagious herpesvirus. Primary infection with the virus results in varicella (chickenpox), whereas reactivation from latency results in herpes zoster (shingles).

Epidemiology

• Transmission occurs by droplet and airborne transmission of infectious respiratory secretions or direct contact with vesicles and respiratory secretions.
• Incubation 10 to 21 days (usually 14 to 16 days) after exposure; cases most contagious 12 days before the rash appears until skin lesions have fully crusted
  • Immunocompromised patients may have longer or shorter incubation.
  • Post–intravenous immunoglobulin (IVIG), incubation may be up to 28 days.
• The attack rate for susceptible household contacts exposed to varicella is 90%.
• Disease is more severe in immunocompromised persons, infants >3 months of age, adolescents, adults, persons with pulmonary disorders (asthma), persons with chronic skin disorders (eczema), and persons on oral and/or IV steroids or long-term aspirin therapy.
• Congenital varicella embryopathy: Risk is 1–2% when maternal primary VZV infection occurs before the 20th week of gestation.
• The incidence of chickenpox has declined by 90% since the introduction of universal varicella vaccination.
• The rate of complications from varicella has declined dramatically since the licensure of the varicella vaccine.

General Prevention

• Varicella vaccine
  • Live attenuated vaccine (Oka strain)
  • 2-dose series for routine immunization of all healthy, susceptible children, adolescents, and adults
• Immunogenicity: 76–85% of immunized children developed protective levels of humoral and cellular immunity after 1 dose, ~100% with 2 doses.
• Effectiveness
  • Effectiveness after 1 dose of vaccine: 86%
  • Effectiveness after 2 doses of vaccine: 98%
  • >97% effective in preventing severe varicella
  • 3.3 times less likely to have breakthrough disease when 2 doses of vaccine (as compared to 1 dose) were administered
• Herpes zoster can occur following varicella vaccination, but clinical severity of the zoster is milder and the risk of acquiring zoster following immunization is lower than following wild-type chickenpox.
• Contraindications
  • Anaphylaxis to vaccine components (e.g., neomycin, gelatin)
  • Pregnant, immunocompromised, or <12 months of age
  • HIV is an exception: Vaccine is recommended for HIV-positive children if CD4+ T-cell counts are ≥15%. Give doses 3 months apart.
  • High-dose corticosteroid doses of ≥2 mg/kg/day or ≥20 mg/day of prednisone, or its equivalent, for ≥14 days are considered immunosuppressive doses: VZV vaccine should not be given until systemic corticosteroid therapy has been discontinued for at least 1 month.
• Postexposure prophylaxis
  • If no contraindication to VZV vaccine: Administer VZV vaccine to susceptible hosts (first or second dose) within 3 days (possibly up to 5 days) of exposure.
  • If contraindications to VZV vaccine exist: Consider passive immunization (see below).
• Give passive immunization if
  • (i) No evidence of immunity in exposed person, (ii) probability that exposure will result in infection, and (iii) likelihood of complications of VZV in the exposed person due to risk factors
  • Susceptible immunocompromised people, pregnant women, and neonates whose mothers develop varicella infection 5 days prior to 2 days after delivery should be especially considered for passive immunization upon exposure.
  • Administer varicella zoster immune globulin (VariZIG^®) or IVIG as per protocol within 10 days of exposure.
  • If VariZIG^® or IVIG is unavailable, some experts recommend postexposure prophylaxis with oral acyclovir (20 mg/kg q6h; max dose: 3,200 mg/24 h) or valacyclovir (20 mg/kg/dose q8h; max dose: 3,000 mg/24 h), beginning 7 to 10 days after exposure and continuing for 7 days.

Pathophysiology

• After primary infection, the virus establishes latency in dorsal root ganglia cells.
• Immunity from natural disease is usually lifelong, but symptomatic and asymptomatic reinfections do occur, boosting antibody levels.