A 2-year-old girl with severe combined immunodeficiency (SCID) awaiting hematopoietic stem cell transplant presents with her parents for immunisation review. She has not received any vaccines since birth due to her condition. According to IAP guidelines, which vaccine should be given IMMEDIATELY before her transplant to provide protection?

Explanation

## Immunisation in Severe Combined Immunodeficiency (SCID) ### Clinical Context Children with SCID have absent or severely defective T-cell and B-cell function. Immunisation strategy must account for: 1. Current severe immunosuppression (contraindication for live vaccines) 2. Future immune reconstitution post-transplant 3. Window of opportunity pre-transplant ### Key Point: **In SCID patients awaiting HSCT, ONLY inactivated vaccines should be given pre-transplant.** Live vaccines are absolutely contraindicated due to severe immunodeficiency. ### IAP Recommendations for SCID Pre-HSCT | Vaccine Type | Pre-HSCT | Post-HSCT (after immune reconstitution) | |---|---|---| | **Inactivated vaccines** | Give 2–4 weeks before HSCT | Repeat after 6–12 months | | **Live vaccines (MMR, Varicella)** | **CONTRAINDICATED** | Give after immune reconstitution (CD4 >200 for ≥3 months) | | **Influenza (inactivated)** | Give annually | Continue | | **Rotavirus** | CONTRAINDICATED | CONTRAINDICATED (age >6 months) | ### High-Yield: **Inactivated influenza vaccine is the ONLY vaccine that should be given to a SCID patient pre-transplant.** It provides protection against a common respiratory pathogen during the vulnerable pre- and post-transplant period. ### Clinical Pearl: - **Timing:** Inactivated vaccines should be given 2–4 weeks before HSCT to allow immune response - **Post-HSCT:** Live vaccines (MMR, Varicella) can be given 6–12 months after transplant once immune reconstitution is confirmed (CD4 >200 cells/μL for ≥3 months) - **Sibling donors:** Vaccinated siblings should avoid live vaccines for 4 weeks post-transplant to prevent transmission of vaccine virus ### Why Each Option is Correct/Incorrect **Inactivated influenza vaccine (CORRECT):** - Inactivated (safe in SCID) - Provides protection against seasonal respiratory pathogen - Should be given pre-HSCT - Reduces morbidity/mortality post-transplant **MMR (WRONG):** - Live attenuated vaccine - Contraindicated in SCID (risk of disseminated measles/mumps/rubella) - Can only be given post-HSCT after immune reconstitution **Varicella (WRONG):** - Live attenuated vaccine - Contraindicated in SCID - Risk of disseminated varicella - Can be given post-HSCT after CD4 recovery **Rotavirus (WRONG):** - Live attenuated vaccine - Contraindicated in SCID - Also age-inappropriate (>6 months) [cite:IAP Immunisation Handbook 2024; Park 26e Ch 8]