Practice question

BCG vaccine is administered via intradermal route which is uniquely specified among routine childhood immunizations. Technique involves injection of small volume 0.05 ml for infants under 12 months and 0.1 ml for older children into superficial dermis of lower insertion of deltoid muscle left arm using 26G or 27G needle inserted bevel upward at approximately 10-15 degree angle pushing needle 2 mm subepidermal creating characteristic peau d orange wheal 6-8 mm bleb that disappears within 30 minutes indicating correct placement. Dermis abundant in Langerhans cells expressing langerin CD207 and dermal CD14+ dendritic cells highly efficient capturing mycobacterial antigens Ag85 complex, migrating to axillary lymph nodes priming Th1 cells secreting interferon gamma activating macrophages forming granuloma containment. Intramuscular or subcutaneous misadministration risks cold abscess formation caseous necrosis, suppurative lymphadenitis, dissemination in immunocompromised and absence of scar considered marker of take. Intradermal route ensures slow depot release, localized induration 2-3 weeks later forming papule ulceration healing with flat 3-7 mm scar visible for life. WHO recommends only intradermal, discouraging jet injectors; training with orange peel simulation and competency assessment mandatory to ensure high coverage scar rates above 90 percent monitoring program quality.