Post-Exposure Varicella Vaccination
Administer the chickenpox vaccine immediately (within 3 days of exposure) to this healthy 12-year-old boy. 1, 2
Rationale for Immediate Vaccination
The varicella vaccine is highly effective as post-exposure prophylaxis when given within 3 days of exposure, with >90% efficacy in preventing chickenpox entirely. 1, 2 Even if administered up to 5 days post-exposure, the vaccine provides approximately 70% efficacy in preventing disease and 100% efficacy in preventing severe disease. 1, 2
Since this exposure occurred only 2 days ago, the child is well within the optimal window for post-exposure vaccination. 1, 2
Why Not the Other Options?
Acyclovir (Option A) - Not Indicated
- Acyclovir prophylaxis protocols for varicella are not established or recommended for healthy children. 3
- Acyclovir is reserved for treatment of active disease in high-risk populations (immunocompromised, neonates, adults with complications), not for routine prophylaxis in healthy children. 3
IVIG/VZIG (Option B) - Wrong Population
- Varicella-zoster immune globulin (VZIG) is indicated only for susceptible individuals with contraindications to vaccination who are at high risk for severe disease (immunocompromised patients, pregnant women, neonates). 1, 2
- This healthy 12-year-old has no contraindications to vaccination, making VZIG inappropriate. 1, 2
- VZIG must be given within 96 hours of exposure, but vaccine is preferred for immunocompetent individuals. 1
Observation (Option D) - Misses Prevention Window
- Simply observing wastes the critical 3-5 day window for effective post-exposure prophylaxis. 1, 2
- Waiting allows preventable disease to develop when a safe, effective intervention is available. 2, 4
Implementation Details
Vaccine administration specifics:
- Give 0.5 mL subcutaneously immediately at this visit. 5
- For a 12-year-old, use single-antigen varicella vaccine (Varivax), as MMRV is only approved through age 12 years. 5
- Schedule the second dose for 3 months later (minimum interval for ages 12 months-12 years). 5
Critical safety consideration:
- Avoid salicylates (aspirin) for 6 weeks after vaccination due to Reye syndrome risk. 2
Evidence Quality
The recommendation for post-exposure vaccination comes from high-quality ACIP guidelines published in MMWR (2007,1999), which explicitly state that varicella vaccine is effective when administered within 3-5 days of exposure. 1 These guidelines are reinforced by research showing 62-79% effectiveness in preventing moderate-to-severe disease when given within 5 days. 6, 4
No evidence indicates that administering vaccine during the presymptomatic or prodromal stage increases adverse events, and if exposure doesn't result in infection, the vaccination provides protection against future exposures. 1