What prophylaxis is recommended for high-risk individuals, such as those with weakened immune systems, pregnant women, or newborns, who have been in contact with someone with chickenpox (varicella-zoster infection)?

Prophylaxis for Chickenpox After Contact

Immediate Action Based on Risk Status

High-risk individuals exposed to chickenpox require varicella-zoster immune globulin (VZIG or VariZIG) administered within 96 hours of exposure, though administration up to 10 days post-exposure remains effective. 1, 2, 3

Who Qualifies as High-Risk

The following groups require post-exposure prophylaxis after significant varicella contact:

Immunocompromised Patients:

• Persons with primary or acquired immunodeficiency disorders 1
• Patients with neoplastic diseases 1
• Those receiving immunosuppressive therapy (>2 mg/kg body weight or >20 mg/day prednisone equivalent) 1
• HIV-infected individuals without evidence of immunity 1
• Bone marrow transplant recipients (regardless of prior varicella history) 1

Pregnant Women:

• Seronegative pregnant women must receive VZIG within 96 hours of exposure 1, 2
• VZIG reduces infection rates from >70% to approximately 30% in susceptible pregnant women 1
• The 96-hour window is critical—effectiveness diminishes significantly after this timeframe 2
• VZIG may prolong the incubation period by up to one week (extending monitoring from 21 to 28 days) 2

Neonates and Infants:

• Newborns whose mothers developed varicella from 5 days before to 2 days after delivery 1, 2
• These neonates require VZIG regardless of whether the mother received it 2
• Premature infants after significant exposure 1
• Infants <1 year of age without evidence of immunity 1

What Constitutes Significant Exposure

Direct contact exposure is defined as:

• Face-to-face indoor contact lasting >5 minutes (some experts suggest >1 hour) 1
• Sharing the same hospital room with an infectious patient 1
• Household exposure (highest risk—85% attack rate in susceptible contacts) 1
• Close contact with playmates or hospital exposure carries approximately 20% of household exposure risk 1

VZIG Administration Protocol

Dosing:

• 125 IU per 10 kg body weight, up to maximum 625 IU 3
• Administered intramuscularly 3

Timing:

• Ideally within 96 hours of exposure 1, 2
• Can be administered up to 10 days post-exposure with similar efficacy (varicella incidence 6.2% when given ≤96 hours vs. 9.4% when given >96 hours to 10 days) 3

Expected Outcomes:

• Varicella incidence after VZIG: 4.5% in immunocompromised patients, 7.3% in pregnant women, 11.5% in infants 3
• VZIG prevents severe maternal disease but does not prevent viremia, fetal infection, or congenital varicella syndrome 2

Alternative: Oral Acyclovir Prophylaxis

When to Consider:

• If VZIG is unavailable 2
• If exposure occurred >96 hours ago 2
• For susceptible pregnant women with risk factors for severe disease who did not receive VZIG 4

Important Limitation:

• Limited data exist regarding acyclovir effectiveness for preventing chickenpox in susceptible HIV-infected or immunocompromised individuals 1
• VZV serology should be performed so acyclovir can be discontinued if patient is seropositive 1

Post-Exposure Vaccination for Eligible Individuals

For immunocompetent persons without evidence of immunity:

• Post-exposure varicella vaccination within 3-5 days may prevent infection or mitigate disease severity 5
• This applies to healthy children and adults who are not immunocompromised 5

Contraindications to vaccination:

• Severely immunocompromised patients 1
• Pregnant women 1
• HIV-infected children except those who are asymptomatic and not immunosuppressed (immunologic category 1) 1

Critical Pitfalls to Avoid

• Failing to act within 96 hours for VZIG in high-risk patients is the most critical error, though administration up to 10 days still provides benefit 2, 3
• Assuming prior varicella history in bone marrow transplant recipients confers immunity—these patients should always be considered non-immune 1
• Withholding VZIG from neonates whose mothers received it—neonates born to mothers with varicella onset 5 days before to 2 days after delivery require VZIG regardless 2
• Using VZIG indiscriminately in low-risk populations when supplies are limited 6

Monitoring After Prophylaxis

• Patients who received VZIG should be monitored for up to 28 days (rather than standard 21 days) due to potential prolongation of incubation period 2
• If varicella develops despite VZIG, treatment with acyclovir should be instituted at earliest signs 1
• Close monitoring is essential as breakthrough infections can still occur, though typically with reduced severity 1, 3

Special Populations Not Requiring Prophylaxis

Individuals with prior varicella or shingles:

• Already immune to VZV and cannot acquire new infection from external exposure 7
• Neither VZIG nor acyclovir prophylaxis is indicated 7
• Do not need to avoid exposure to chickenpox or shingles 7