BCG Scar Recognition

Please read through the following module. Further information can be obtained via the reference sites at the end of the module. Complete the quiz once you have read through the module.

Aims and Objectives

By the end of this module, you will:

  1. Have knowledge and understanding of the BCG vaccine
  2. Know how the vaccine is administered and the process of scar formation.
  3. Know how to identify BCG scars and the process for checking scars
  4. Know how to distinguish between BCG scars and small pox scars


Background Information

What is TB?

Tuberculosis (TB) is caused by the bacterium, Mycobacteria tuberculosis, which is mainly transmitted via respiratory droplets i.e. through coughing, sneezing. It is the second greatest killer due to a single infectious agent worldwide (after HIV). The WHO estimates that one third of the world’s population have latent TB (infection without symptoms). The highest rates of infection are found in South and South East Asia and Sub Saharan Africa.

In the UK, the highest risk of TB is in people born in countries with high incidence.

In adults, TB of the lung is the commonest (and most infectious) form, but TB can affect any organ of the body.


BCG Vaccine

Bacillus Calmette-Guerin (BCG) contains a live, attenuated strain of Mycobacterium bovis, which provides cross immunity to Mycobacterium tuberculosis and Mycobacterium leprae (causes leprosy in humans). The vaccine has been in existence since 1921 and was introduced into the WHO Expanded Programme on Immunisation in 1974, leading to global coverage of over 80% in endemic countries.

The vaccine was introduced in the UK in 1953 when school children were routinely vaccinated. However, as the incidence of TB declined in the indigenous population, the vaccine was removed from the childhood immunisation programme. It is now only administered to babies born to parents from high prevalence countries.

The effectiveness of the vaccine varies in different studies. However, meta-analysis shows that the vaccine is 70-80% effective against the most severe forms of TB such as TB meningitis, which tends to occur in children. It is less effective against the respiratory form of the disease. Protection is thought to be between 10 to15 years; data after this time is limited and it is thought protection is likely to wane.


Administration and Local Reactions

The BCG vaccine should be administered intradermally only to the deltoid insertion region of the left upper arm. The left arm is the WHO recommended site and is therefore, the internationally recognised site of the BCG scar. Sites other than the arm are not recommended due to increased risk of TB lymphadenitis (TB infection of the lymph nodes). Some countries administer the vaccine percutaneously and it is thought that this might affect the scar formation.

When the vaccine is administered intradermally, a tense, blanched, raised bleb forms at the site. This, then becomes a small papule (raised red spot) in 90-95% of cases 2 or more weeks later. This may ulcerate and then subsides over several weeks or months to heal, leaving a small, flat scar, often with a raised central area when palpated (see figure 1).

Individuals may have severe local reactions to the vaccine, including abscess, large ulcers and keloid formation, which will affect the eventual scar formation.


Identification of BCG scars

Screening for or evidence of TB immunity is required for all health care workers due to the increased risk of exposure.

Evidence of BCG vaccination includes the following

  • Documentary evidence of vaccination
  • Clear and reliable history of vaccination
  • Evidence of characteristic scar (figure 1).

Ideally, all three are required for evidence of vaccination and documentary evidence should always be sought in all cases when clients attend for BCG scar check. However, clients might not have documentary evidence of vaccination, particularly if they were born overseas and were vaccinated as infants (as is the case in most endemic countries). In these circumstances, they might not be able to reliably recall the vaccination. Providing a clear and reliable history of vaccination is not enough in the absence of documentary evidence and a visible scar, Therefore, often the presence of the characteristic scar is the only evidence that BCG vaccination has been performed.

Scar Check

Ask the client if they have a BCG scar and follow the procedure outlined below.

  • Check the scar under good lighting
  • Initially inspect the scar:
    • Position- should be left upper arm, either centrally or the posterior lateral or anterior medial aspect of the arm. Less commonly, the scar might be located in the right upper arm and rarely thigh or forearm.
    • Appearance-usually circular in shape, but can be oval or even linear. The scar is typically raised.
  • Palpate the scar to feel the central raised area, either central region or uniformly.

If the client is unsure if they have a BCG scar, then:

  • Check both upper arms and then the thigh for characteristic features as above.


Reasons for absence of characteristic scar:

  • Scar not formed following intradermal injection (unusual).
  • Vaccine administered percutaneously (some countries such as Japan prefer this route), therefore characteristic scar not formed.
  • Non standard administration site used (i.e. site other than upper arm and typically the left arm).

When there is an unclear vaccination history and no characteristic scar, further BCG vaccination must not be administered as this increases the risk of adverse reactions. In these individuals, they should be referred first for Mantoux testing or Quantiferon Gold Testing.


Figure 1: BCG Scar



Distinguishing BCG from Small pox scar

The smallpox vaccine is routinely given in the deltoid region of the arm and also leaves a scar. Therefore, it can be confused for the BCG vaccine. Clients may also have been immunised with both vaccines and have the individual scars on the same arm. The smallpox vaccine is given in an entirely different manner to the BCG vaccine. The vaccine is given using a bifurcated (two-pronged) needle that is dipped into the vaccine solution. When removed, the needle retains a droplet of the vaccine. The needle is used to prick the skin a number of times in a few seconds. The pricking is not deep, but it will cause a sore spot and one or two droplets of blood to form. This method givens the scar its typical appearance with a central depression and lines radiating out (similar to a bicycle wheel). The differences between the scars of the small pox vaccine and the TB vaccine can be seen in Figure 2 and 3. The small pox vaccine is no longer routinely administered following the eradication of small pox in 1979.

Figure 2: Small Pox Scar



Figure 3: BCG scar versus Smallpox Scar


Figure 4: BCG scar versus Smallpox scar:



Now complete the Quiz on BCG Scar Recognition below


1) Department of Health: Immunisation against Infectious Disease, Chapter 32-Tuberculosis, accessed via

2) Health Protection Agency: Tuberculosis Fact sheet, accessed via

3) World Health Organisation-Immunological Basis for Immunisation Series Module TB 2011, accessed via

4) World Health Organisation-BCG vaccination, accessed via

5) World Health Organisation-Tuberculosis Fact sheet accessed via

6) Centre for Disease Control (CDC)-Tuberculosis vaccination, accessed via


BCG Scar Recognition Quiz

  • 4

  • 5

  • b

  • c

  • d

  • e

  • 6A) Identify the correct BCG and Smallpox scars on the following pictures:

  • Enter either "BCG" or "Smallpox" in both fields
  • e

  • 6B

  • Enter either "BCG" or "Smallpox" in both fields
  • e

  • 6C

  • Enter either "BCG" or "Smallpox" in both fields
  • e

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