Write a short note on BCG Vaccine.

Definition

BCG (Bacille Calmette-Guérin) is a live attenuated vaccine (from Mycobacterium bovis) that protects children against the severe forms of tuberculosis (miliary TB and TB meningitis).

Administration

• Given at birth (or at first contact) as part of the UIP.
• Intradermal injection of 0.05 mL (newborn) / 0.1 mL (older) over the left upper arm (deltoid).
• A correct intradermal dose produces a wheal, then over weeks a papule → ulcer → healed scar (a marker of successful vaccination).

Complications

• Local — injection abscess, prolonged ulceration, regional (axillary) lymphadenitis.
• Disseminated BCG (BCG-osis) in immunocompromised infants — hence caution in known immunodeficiency.

Mechanism & Efficacy

BCG induces cell-mediated immunity against mycobacteria; it does not reliably prevent primary infection or adult pulmonary TB but substantially reduces severe disseminated forms (miliary TB, TB meningitis) in young children.

Complications in Detail

• Most complications are local and self-limiting (abscess, ulcer, small lymph node).
• Suppurative lymphadenitis may need aspiration; disseminated BCG requires anti-tubercular therapy and immunological evaluation.

Key Points Recap

• Live attenuated; intradermal; protects against severe childhood TB; forms a scar.
• Caution/avoid in significant immunodeficiency (disseminated BCG risk).

Programme Note

BCG is one of the most widely used vaccines worldwide and is given as early as possible after birth in high-TB-burden countries such as India, because it prevents the most dangerous childhood forms of tuberculosis.

Exam Relevance

This is a frequently asked short note — remember the vaccine type/route, its place in the UIP schedule, and its key precautions or programmatic significance.

Protects against miliary TB and TB meningitis, not pulmonary TB.