What is the recommended post-exposure prophylaxis (PEP) for pediatric patients exposed to varicella who are not immune?

Varicella Post-Exposure Prophylaxis in Pediatric Patients

For pediatric patients exposed to varicella without immunity, VariZIG (varicella-zoster immune globulin) should be administered as soon as possible and within 10 days of exposure at a dose of 125 IU/10 kg body weight up to a maximum of 625 IU. 1

Patient Selection for VariZIG

VariZIG is indicated for the following high-risk pediatric populations without evidence of immunity:

• Immunocompromised patients 1
• Newborn infants whose mothers have signs and symptoms of varicella around delivery (5 days before to 2 days after) 1
• Hospitalized premature infants born at ≥28 weeks of gestation whose mothers lack evidence of immunity 1
• Hospitalized premature infants born at <28 weeks of gestation or weighing ≤1,000 g at birth, regardless of maternal immunity status 1

Timing of Administration

The timing of VariZIG administration is critical:

• Optimal effectiveness: Within 96 hours (4 days) of exposure 1
• Extended window: Up to 10 days post-exposure 1, 2

Research shows that administration of immune globulins with high levels of anti-varicella-zoster virus antibodies beyond 4 days (up to 10 days) results in comparable incidence of varicella and disease attenuation compared to administration within the first 4 days 1, 3. In a large expanded-access program, varicella incidence was similar when comparing VariZIG administration ≤96 hours vs. >96 hours (up to 10 days) post-exposure (6.2% vs. 9.4%) 3.

Dosing Guidelines

• VariZIG dose: 125 IU/10 kg body weight, administered intramuscularly 1
• Maximum dose: 625 IU (five vials) 1
• Minimum dose: 62.5 IU (0.5 vial) for patients weighing ≤2.0 kg and 125 IU (one vial) for patients weighing 2.1–10.0 kg 1

Alternative Prophylaxis Options

When VariZIG is unavailable or administration window has passed:

1. Acyclovir prophylaxis: Some experts recommend acyclovir 20 mg/kg body weight (maximum 800 mg) per dose orally 4 times daily for 5-7 days 1, 2

However, recent evidence suggests that acyclovir may be less effective than VariZIG. A retrospective cohort study found that the proportion of patients who subsequently developed varicella was highest with acyclovir (15.4%) compared to VariZIG (3.4%) 4.

Post-Prophylaxis Monitoring

• Monitor for signs and symptoms of varicella for 28 days after exposure 1, 2
• VariZIG may prolong the incubation period by ≥1 week 1
• Initiate antiviral therapy immediately if signs or symptoms of varicella occur 1

Special Considerations

• For patients eligible for vaccination, varicella vaccine should be administered ≥5 months after VariZIG administration 1
• Patients receiving monthly high-dose IGIV (>400 mg/kg) within 3 weeks before exposure likely do not require VariZIG 1, 2
• For high-risk patients with additional exposures to varicella-zoster virus ≥3 weeks after initial VariZIG administration, another dose of VariZIG should be considered 1, 2

Safety Profile

VariZIG is generally well-tolerated with the most common adverse reactions being:

• Pain at injection site (2%) 1
• Headache (2%) 1

Contraindications include:

• History of anaphylactic or severe systemic reactions to human immune globulins 1
• IgA-deficient patients with antibodies against IgA and history of hypersensitivity 1

By following these guidelines, clinicians can effectively prevent or attenuate varicella infection in susceptible pediatric patients following exposure, significantly reducing morbidity and mortality in these high-risk populations.