What is the recommended post-exposure prophylaxis (PEP) for chickenpox?

Post-Exposure Prophylaxis for Chickenpox

For individuals exposed to chickenpox (varicella), varicella-zoster immune globulin (VariZIG) should be administered as soon as possible and within 10 days of exposure for susceptible high-risk individuals, while varicella vaccination is recommended within 3-5 days of exposure for eligible individuals without contraindications. 1, 2

Assessment of Immunity Status

Before determining the appropriate post-exposure prophylaxis (PEP), assess evidence of immunity:

• History of documented varicella disease
• Laboratory evidence of immunity or confirmed disease
• Documentation of age-appropriate vaccination
• Birth in the United States before 1980 (only for immunocompetent, non-pregnant patients) 2

Post-Exposure Prophylaxis Options

1. Varicella-Zoster Immune Globulin (VariZIG)

Indications:

• Immunocompromised individuals without evidence of immunity
• Pregnant women without evidence of immunity
• Newborns whose mothers developed varicella between 7 days before and 7 days after delivery 3
• Hospitalized premature infants (≥28 weeks gestation) whose mothers lack evidence of immunity
• Hospitalized premature infants (<28 weeks gestation or ≤1,000g birth weight), regardless of maternal immunity status 1

Administration:

• Administer as soon as possible, optimally within 96 hours but effective up to 10 days post-exposure 1, 3
• Dosage: 125 IU/10 kg body weight (maximum 625 IU), administered intramuscularly 1
• Monitor for 28 days after exposure (VariZIG can extend incubation period) 1

2. Varicella Vaccination

Indications:

• Healthy individuals ≥12 months of age without evidence of immunity
• Not contraindicated for immunocompetent individuals

Administration:

• Administer within 3-5 days of exposure
• Effectiveness: 62-90% in preventing infection or reducing severity 4, 1
• For adults and children who have received one dose previously, administer second dose if ≥4 weeks since first dose 2

3. Acyclovir Prophylaxis

Indications:

• When VariZIG is unavailable or beyond the 10-day window
• May be considered for immunocompromised patients when VariZIG is not available

Administration:

• Dosage: 20 mg/kg (maximum 800 mg) orally 4 times daily for 5-7 days 1, 5
• Begin within 7-10 days of exposure

Management Based on Exposure Type and Immunity Status

Healthcare Workers (HCW)

1. HCW with 2 doses of vaccine:

   • Monitor daily during days 8-21 post-exposure
   • Report fever, skin lesions, or systemic symptoms immediately
   • Exclude from work if symptoms develop 2

2. HCW with 1 dose of vaccine:

   • Receive second dose within 3-5 days after exposure (if ≥4 weeks since first dose)
   • If second dose not received or given >5 days post-exposure, exclude from work for 8-21 days 2

3. Unvaccinated HCW without immunity:

   • Potentially infectious from days 8-21 post-exposure
   • Should be furloughed during this period
   • Receive post-exposure vaccination as soon as possible 2

4. HCW with contraindications to vaccination:

   • Administer VariZIG
   • Extend work restriction period to 28 days due to prolonged incubation period 2

Immunocompromised Patients

• VariZIG is the preferred prophylaxis 2
• If VariZIG unavailable, consider acyclovir prophylaxis 1
• Monitor closely for 28 days for development of varicella 1

Special Considerations

1. Timing is critical:

   • Efficacy of PEP decreases with time after exposure
   • VariZIG most effective within 96 hours but can be given up to 10 days 1, 3
   • Vaccination most effective within 3-5 days 4

2. Significant exposure definition:

   • Household contact (highest risk with 65-100% attack rate)
   • Face-to-face contact for >5 minutes
   • Hospital room sharing
   • Direct contact with lesions 1

3. Common pitfalls to avoid:

   • Delaying prophylaxis while waiting for serology results
   • Assuming adults born before 1980 are immune if they are immunocompromised or pregnant
   • Failing to recognize that VariZIG extends the incubation period to 28 days

Follow-up After Prophylaxis

• Monitor for signs and symptoms of varicella for 21 days (28 days if VariZIG was administered)
• Initiate antiviral treatment immediately if symptoms develop
• For those receiving VariZIG, delay varicella vaccination for at least 5 months 1

By implementing appropriate post-exposure prophylaxis based on exposure risk, immune status, and timing since exposure, the risk of varicella infection and its complications can be significantly reduced.