BCG Vaccine
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Direct answer
The BCG vaccine is a live attenuated Mycobacterium bovis preparation given intradermally in infancy to protect against severe childhood tuberculosis, mainly tuberculous meningitis and miliary disease. It is a single early dose, and its usual complications are local ulceration and suppurative lymphadenitis rather than systemic illness.
What you must remember
- Strain: a live attenuated Mycobacterium bovis strain, with the Danish 1331 strain being the one most often cited in textbooks.
- Dose and route: 0.05 mL intradermally up to 1 month of age and 0.1 mL thereafter.
- Site and timing: the left upper arm in the Indian UIP schedule, ideally at birth or as early as possible within the first year.
- Expected scar: a papule within two to three weeks that ulcerates and heals over about three months, leaving a small scar.
- Lymphadenitis: suppurative axillary or cervical nodes, typically appearing weeks to months after vaccination.
- Management: most nodes resolve without treatment, and large abscesses are aspirated rather than incised.
- Contraindication: symptomatic HIV infection and severe immunodeficiency, because the live vaccine can disseminate.
- Protection: the main benefit is against severe childhood forms of tuberculosis, while protection against adult pulmonary disease is variable.
Recognising the normal reaction from the complications
A week-old infant receives BCG, and the parents ask what the mark on the arm means. Each reaction has a predictable course, and the exam expects you to separate the normal local response from the complications.
| Reaction | Typical course | Management |
|---|---|---|
| Local papule and ulcer | Papule in 2 to 3 weeks, healing in about 3 months | Keep clean, no treatment |
| Suppurative lymphadenitis | Axillary or cervical node, weeks to months later | Usually self-limiting, aspirate large abscesses |
| BCG osteitis | Bone infection, usually months after vaccination | Anti-tubercular therapy with specialist input |
| Disseminated BCG | Infants with severe immunodeficiency | Urgent treatment and immunodeficiency evaluation |
Only the local reaction is expected, so the other rows are the complications examiners test. Disseminated disease in an infant should prompt a search for severe combined immunodeficiency. Lymphadenitis is the complication most often tested, and its management separates a careful answer from a risky one. Books differ on whether the scar predicts protection, so a missing scar should not be read as proof of vaccine failure.
Where the exam tries to catch you
Most BCG questions hinge on the management of complications and the contraindications.
- Trap: incising a suppurating BCG node to drain it Correct: aspiration or observation is preferred, because incision can leave a persistent discharging sinus.
- Trap: withholding BCG from every HIV-exposed child Correct: symptomatic HIV is a contraindication, while asymptomatic HIV-exposed infants are managed according to national policy.
- Trap: expecting BCG to prevent adult pulmonary tuberculosis reliably Correct: its established benefit is protection against severe childhood forms, and adult protection varies between studies.
Frequently asked questions
What is the dose and route of BCG for an infant?
An infant receives 0.05 mL of BCG given intradermally in the left upper arm in the Indian UIP schedule, ideally at birth. Infants older than one month receive 0.1 mL.
What does the expected BCG scar look like?
A small papule appears within two to three weeks, becomes an ulcer, and heals over about three months to leave a small scar. This ulcer is the expected local reaction and needs only keeping clean.
How is BCG lymphadenitis managed?
Suppurative lymphadenitis after BCG usually resolves without treatment. Large fluctuant nodes are managed by needle aspiration, because incision of BCG lymphadenitis can leave a persistent discharging sinus.
Which infants should not receive the BCG vaccine?
Infants with symptomatic HIV infection and those with severe immunodeficiency should not receive BCG, because the live vaccine can cause disseminated disease. Asymptomatic HIV-exposed infants are handled according to national policy.
Why does the Indian programme give BCG at birth?
Early vaccination protects infants during the years when severe childhood tuberculosis is most likely to occur. The Universal Immunization Programme therefore gives BCG at birth or as early as possible within the first year of life.