At what time post-exposure should varicella vaccine be administered to children over 6 and 12 months?

Varicella Post-Exposure Prophylaxis Timing for Children 6-12+ Months

Varicella vaccine should be administered within 3 days (72 hours) of exposure to varicella for optimal post-exposure prophylactic effect in children ≥12 months of age, while children 6-12 months are not eligible for post-exposure vaccination. 1, 2

Eligibility by Age Group

Children 6-12 Months

• Varicella vaccine is NOT approved for children under 12 months of age
• These infants are not eligible for post-exposure vaccination
• Alternative prophylaxis with varicella zoster immune globulin should be considered for high-risk infants in this age group 1

Children ≥12 Months

• Eligible for post-exposure prophylaxis with varicella vaccine
• Timing is critical for effectiveness:
  • Most effective when given within 3 days (72 hours) of exposure 2
  • May provide some benefit when given up to 5 days post-exposure, but with reduced effectiveness 3
  • Administration beyond 5 days post-exposure is not recommended specifically for post-exposure prophylaxis

Effectiveness of Post-Exposure Vaccination

• When administered within 3 days of exposure:

  • 95.2% effective for prevention of any disease 2
  • 100% effective for prevention of moderate or severe disease 2
  • Even when breakthrough infection occurs, disease severity is significantly reduced 4

• Effectiveness decreases when administered after 3 days:

  • Vaccine effectiveness for preventing moderate or severe disease is 77% when given within first 3 days post-exposure 4
  • Limited data exists on effectiveness beyond 3 days 3

Administration Guidelines

For children 12 months to 12 years:

• First dose should be given as soon as possible after exposure (ideally within 72 hours) 5
• If this is the first dose, a second dose should be scheduled with minimum interval of 3 months 5
• If the child has already received one dose previously, the second dose can be administered if at least 28 days have passed since the first dose 5

For persons ≥13 years:

• First dose should be given as soon as possible after exposure (ideally within 72 hours)
• Second dose should be administered 4-8 weeks later 5

Important Considerations

• Post-exposure vaccination should only be given to those without evidence of immunity 6

• Evidence of immunity includes:

  • Documentation of age-appropriate vaccination
  • Laboratory evidence of immunity or disease
  • Healthcare provider-verified history of varicella or zoster 6

• Contraindications:

  • Pregnancy
  • Severe immunocompromise
  • Severe allergic reaction to vaccine components 6
  • Children under 12 months of age 5

Clinical Pearls

• Post-exposure vaccination not only prevents disease but can significantly attenuate severity if breakthrough infection occurs 4, 2
• Vaccine is highly effective in preventing outbreaks in congregate settings when used promptly after exposure 2
• The decision to vaccinate post-exposure should not delay routine vaccination at recommended ages (12-15 months for first dose, 4-6 years for second dose) 5
• For children who are not eligible for vaccination (under 12 months or immunocompromised), varicella zoster immune globulin should be considered for post-exposure prophylaxis 1