What Is a BCG Vaccination
, by Andrew Odgers, 8 min reading time
Vaccine Guide
What Is a BCG Vaccination?
BCG stands for Bacillus Calmette-Guerin, a live-attenuated vaccine derived from Mycobacterium bovis that provides protection against tuberculosis and some related infections. It is one of the oldest vaccines still in widespread global use and remains an important part of the UK immunisation programme for specific high-risk groups.
1921Year BCG first used in humans
100M+BCG doses given globally each year
70–80%UK efficacy against severe TB in children
LifetimeDuration of protection from a single dose
What BCG protects against
The scope of BCG vaccine protection
Tuberculosis
BCG is most effective against severe forms of TB in children, including TB meningitis (inflammation of the brain coverings caused by TB) and miliary TB (widespread blood-borne TB). UK studies show efficacy of 70 to 80 percent against these severe forms. Protection against pulmonary TB in adults is more variable, estimated at 50 to 80 percent depending on the study population and geographic location. BCG is most effective when given to children who have not previously been exposed to environmental mycobacteria, which is why it works better in some UK populations than in populations with high environmental mycobacteria exposure.
Leprosy and Buruli ulcer
BCG provides partial protection against leprosy, the chronic infectious disease caused by Mycobacterium leprae, and against Buruli ulcer, caused by Mycobacterium ulcerans. These conditions are uncommon in the UK but relevant for travellers and individuals from endemic regions.
Non-specific immune effects
Epidemiological evidence suggests that BCG vaccination is associated with reduced overall infant mortality in high-burden countries, beyond its specific effects against TB. This non-specific effect may reflect broader training of the innate immune system. Research into the mechanisms of this non-specific protection has informed emerging research on trained immunity as a concept.
Who receives BCG in the UK
TrueCurrent NHS BCG programme
BCG vaccination: what to expect
The process, the reaction, and the scar
How BCG is administered
BCG is administered as an intradermal injection — very different from the intramuscular route used for most other vaccines. The injection is given into the dermis of the skin, typically over the left upper arm deltoid area, using a 26 gauge needle at a very shallow 10 to 15 degree angle. A small bleb (raised area) of 5 to 7 mm diameter should form at the injection site, confirming correct intradermal delivery. If no bleb forms, the injection may have been subcutaneous and may need to be repeated.
The expected skin reaction
In the weeks following BCG vaccination, the injection site undergoes a characteristic sequence of changes. A small red papule appears at 2 to 6 weeks, which may develop into a pustule (blister containing fluid) that breaks open and crusts. This process typically takes 6 to 12 weeks to complete. Once healed, a small scar remains — this is the classic BCG scar and confirms that the vaccine has been administered and has produced the expected local reaction.
What is and is not a cause for concern
The entire process from papule to healed scar is expected and should not be treated as an infection or adverse event. The site should not be covered tightly, squeezed, or treated with antiseptics unless specifically advised. If the lymph nodes in the armpit on the vaccinated side become significantly swollen (larger than 1 cm), soft, or if there is marked swelling and pain, contact the GP. Significant axillary lymphadenopathy after BCG is uncommon but occurs and should be assessed.
Global BCG programmes vs UK selective use
TrueWhy different countries use BCG differently
Frequently asked
Questions answered
Does BCG protect against COVID-19?
There was significant early interest in whether BCG's non-specific immune training effects might provide protection against COVID-19. Multiple randomised controlled trials investigated this, including BRACE (Australia) and others in Europe and Africa. The results have not demonstrated a clinically meaningful protective effect against COVID-19 from BCG vaccination. BCG should not be relied upon for COVID-19 protection.
Can adults receive BCG if they never had it as a child?
Yes, subject to a prior tuberculin skin test. Adults who have never received BCG and who have not previously been exposed to TB are eligible for BCG vaccination. A tuberculin skin test (Mantoux test) must be performed first, and BCG should only be given to those who test negative (no prior exposure). A positive tuberculin test indicates prior TB exposure or prior BCG, both of which are contraindications for BCG vaccination.
Is the BCG scar proof of immunity?
A BCG scar confirms that the vaccine produced the expected local reaction and was administered correctly. It does not directly measure immunity. Some vaccinated individuals who do develop a scar may still have limited immunity, and scar size does not correlate reliably with protection. The scar is a marker of vaccination, not a precise measure of immune status.
Can BCG be given at the same time as other vaccines?
BCG must not be given at the same site as other vaccines, and cannot be given simultaneously with other live vaccines (except MMR, which may be given simultaneously at different sites). If BCG is given first, other live vaccines should be delayed by at least 4 weeks. This is because live vaccine interactions could theoretically interfere with each other's immune responses.
Vaccination supplies
Clinical vaccination consumables from Charles Medical
Charles Medical supplies hypodermic needles, syringes, and all consumables used in vaccination practice. Next-day UK delivery, no minimum order.