What is the recommended post-exposure prophylaxis for individuals at high risk of severe varicella (chicken pox) who have been exposed to chicken pox, including pregnant women and immunocompromised individuals?

Post-Exposure Prophylaxis for Chickenpox

For immunocompetent individuals without evidence of immunity, administer varicella vaccine within 3 days of exposure (>90% effective at preventing disease), or up to 5 days post-exposure (70% effective at preventing disease, 100% effective at preventing severe disease); for high-risk individuals with contraindications to vaccination—including pregnant women, immunocompromised patients, and newborns of mothers with peripartum varicella—administer varicella-zoster immune globulin (VZIG/VariZIG) within 96 hours of exposure. 1, 2

Evidence of Immunity Criteria

Before determining prophylaxis strategy, establish immune status using these criteria 3:

• Documentation of age-appropriate vaccination (2 doses for children/adults) 2
• Laboratory evidence of immunity (positive antibody titers) 2
• Confirmed history of prior varicella disease 2
• Birth in the United States before 1980 (only for non-immunocompromised, non-pregnant individuals) 3

Post-Exposure Prophylaxis Algorithm

For Immunocompetent Individuals Without Evidence of Immunity

Varicella vaccine is the preferred post-exposure prophylaxis 1, 2:

• Within 3 days of exposure: Administer varicella vaccine immediately—this provides >90% efficacy in preventing varicella entirely 3, 1
• Within 5 days of exposure: Vaccine still provides benefit with approximately 70% efficacy in preventing disease and 100% efficacy in preventing severe disease 3, 1
• Beyond 5 days: Vaccination is still indicated as it provides protection against future exposures (if current exposure did not cause infection) 3

For previously vaccinated individuals 3:

• One prior dose: Administer second dose within 3-5 days of exposure (if ≥4 weeks have elapsed since first dose) 3
• Two prior doses: No additional vaccination needed; monitor for breakthrough disease 3

For High-Risk Individuals With Contraindications to Vaccination

Varicella-zoster immune globulin (VariZIG) is indicated for 3, 2:

• Pregnant women without evidence of immunity 3, 2
• Immunocompromised patients (oncologic conditions, primary immunodeficiency, solid organ transplant, hematopoietic cell transplant, patients on immunosuppressive therapy) 3, 2, 4
• Newborns whose mothers developed varicella from 5 days before to 2 days after delivery 2
• Premature infants (≥28 weeks gestation if mother lacks immunity; <28 weeks or ≤1000g regardless of maternal immunity) 5

VariZIG administration details 3:

• Timing: Administer as soon as possible, ideally within 96 hours of exposure for maximum benefit 3, 2
• Dosing: Intramuscular administration per product guidelines 3
• Availability: Obtained through FFF Enterprises (1-800-843-7477) under Investigational New Drug Application Expanded Access protocol 3
• Effect on incubation: May prolong incubation period by one week, extending monitoring period from 21 to 28 days 3

Clinical outcomes with VariZIG: Real-world data from 303 immunocompromised patients showed varicella infection rates of only 6-7% after VariZIG administration, with most breakthrough cases being mild and no varicella-related deaths 4

Alternative for Immunocompromised Patients

Antiviral prophylaxis with acyclovir/valacyclovir may be considered when VZIG is unavailable or as an alternative strategy 6:

• Recent pediatric data showed only 2.2% secondary infection rate with antiviral PEP versus 20% without prophylaxis (p=0.036) 6
• Dosing: Standard prophylactic dosing (specific regimens not established in guidelines, but treatment doses from FDA label: acyclovir 800mg 4 times daily for immunocompetent adults, IV acyclovir for immunocompromised) 7
• Timing: Initiate within days of exposure and continue through incubation period 6
• No significant adverse events reported in immunocompromised patients receiving antiviral PEP 6

Post-Exposure Monitoring and Isolation

For Vaccinated Individuals After Exposure

Monitor daily during days 8-21 post-exposure for 3, 2:

• Fever
• Skin lesions (any atypical rash)
• Systemic symptoms (headache, constitutional symptoms)

Exclude from work/school immediately if symptoms develop 3

For Unvaccinated Susceptible Individuals

Healthcare personnel 3:

• Furlough from days 8-21 after exposure (potentially infective period) 3
• If VZIG administered, extend exclusion through day 28 3

General population 2:

• Exclude from institutions for 21 days after rash onset in last case 2

Critical Safety Considerations

Avoid salicylates for 6 weeks post-vaccination due to Reye syndrome risk 1

Immune globulin interference: Do not administer varicella vaccine for 3-11 months after receiving blood products or immune globulin, as passively transferred antibodies may inhibit vaccine response 1

No increased risk from vaccination during incubation: No evidence indicates that administering vaccine during presymptomatic or prodromal stages increases adverse events 3, 1

Common Pitfalls to Avoid

Do not delay vaccination while awaiting antibody testing—if exposure occurred and immunity is uncertain, vaccinate immediately within the 3-day window for optimal efficacy 1, 2

Do not assume birth before 1980 equals immunity in pregnant or immunocompromised patients—this criterion only applies to immunocompetent, non-pregnant individuals 3

Do not withhold VZIG beyond 96 hours thinking it's too late—while optimal within 96 hours, some benefit may still occur if given slightly later, particularly in high-risk patients 3

For healthcare settings, prioritize pre-exposure vaccination—post-exposure vaccination is a backup strategy; all healthcare personnel should be vaccinated before employment 3, 2