What is the recommended post-exposure prophylaxis for immunocompromised adults exposed to varicella-zoster virus (VZV)?

Post-Exposure Prophylaxis for Immunocompromised Adults Exposed to Varicella-Zoster Virus

Immunocompromised adults exposed to varicella-zoster virus should receive VariZIG (varicella-zoster immune globulin) as soon as possible but within 96 hours of exposure at a dose of 125 units/10 kg body weight up to a maximum of 625 units.

Assessment of VZV Exposure

Before administering post-exposure prophylaxis, determine if a significant exposure has occurred:

• Significant exposure definition: Face-to-face indoor contact with an infectious person
  • Duration of contact: Experts differ between >5 minutes to >1 hour 1, 2
  • Does not include transitory contact
• Sources of exposure:
  • Individuals with varicella (chickenpox)
  • Individuals with disseminated herpes zoster
  • Individuals with uncovered lesions of localized herpes zoster

Determining Immunity Status

Assess immunity status of the exposed immunocompromised individual:

• Evidence of immunity:
  • Documented receipt of 2 doses of varicella vaccine
  • Laboratory evidence of immunity
  • Documented history of varicella or herpes zoster
  • Note: Bone marrow transplant recipients should be considered non-immune regardless of previous history 1

Post-Exposure Prophylaxis Protocol

First-Line: VariZIG Administration

• Timing: Administer as soon as possible but within 96 hours after exposure 1, 2
• Dosage: 125 units/10 kg body weight, up to maximum of 625 units (5 vials) 1, 2
• Administration route: Intramuscular injection
• Duration of protection: Approximately 3 weeks (one half-life of immunoglobulin) 1, 2
• Note: VariZIG may extend the incubation period from 10-21 days to >28 days 1

Special Considerations

• Patients on IGIV: Those receiving monthly high-dose immune globulin intravenous (>400 mg/kg) likely do not require VariZIG if the last dose was administered <3 weeks before exposure 1, 2
• Repeated exposure: If re-exposed >3 weeks after initial VariZIG dose, another full dose should be administered 1
• Monitoring: Monitor for signs of varicella for 28 days after exposure (extended incubation period)

Alternative Approaches

• Acyclovir: While not FDA-approved for post-exposure prophylaxis in immunocompromised patients, some evidence suggests it might be considered if VariZIG is unavailable 3, 4
  • Limited data shows effectiveness of acyclovir/valacyclovir as PEP in immunocompromised patients, with significantly lower rates of secondary VZV infection compared to no prophylaxis (2.2% vs 20.0%, p=0.036) 4
  • If used, patients should be closely monitored for early signs of infection 2

Important Caveats

• VariZIG is not effective for:
  • Treating established clinical varicella or herpes zoster
  • Preventing disseminated zoster 1, 2
• VariZIG is available in the US through an Investigational New Drug Application Expanded Access protocol 1
• Early treatment with acyclovir should be initiated if varicella develops despite prophylaxis

Infection Control Measures

• Implement airborne and contact precautions for patients with varicella or disseminated herpes zoster 1
• Only healthcare personnel with evidence of immunity should care for patients with confirmed or suspected VZV infection 1
• Maintain precautions until all lesions are dry and crusted 1

By following this protocol, the risk of severe varicella infection in immunocompromised adults can be significantly reduced, decreasing morbidity and mortality associated with VZV infection in this vulnerable population.