Why does the BCG vaccine cause a wound

QUESTION: Why does the BCG vaccine cause a wound?

Quick Answer

BCG causes a reaction in the skin where it is given. This shows that the vaccine has worked and the child’s body is becoming protected from some serious forms of tuberculosis.

Why does the BCG vaccine cause a wound? To answer that, we need to know how the BCG vaccine works

The BCG vaccine contains live attenuated Mycobacterium bovis. Mycobacterium bovis is a  bacteria that is closely related to the one that causes tuberculosis (TB) in humans. The term attenuated means that while the bacteria used in the vaccine is live, it has been effectively made scientifically harmless. 

Since it is looks similar to the bacteria that causes TB, following intradermal injection (within the skin)  the BCG vaccine stimulates the body to fight it using a local immune response. This response in most children results in an ulcer or wound and even, commonly, a blister . When this wound heals over 1 to 6 weeks, it leaves a flat permanent scar at the injection site.

How this skin lesion behaves has been shown to depend on many factors, notably, the dose that gets administered. For example, if the dose of the vaccine is  halved, the size of the scar will decrease by approximately 1 mm. Also, vaccines with low viability result in smaller scars compared to vaccines with high viability.

What’s important for parents to know is that the presence of the scar means that the defenses of your child’s body are active against the foreign body. And this is a good thing.

Indeed, a 2020 study conducted in Guinea Bissau showed that among BCG-vaccinated children, those who develop a scar, have 39 % (26–49 %) lower mortality compared with those who do not develop a scar.

Patient Information

I regret that you might not trust us, but please know that the recommendations we are making are made all over the world. While in Africa vaccine coverage is often limited, some countries are lucky to give even more vaccines to their children.

  • I would like you to trust us because we have your child’s best interests at heart. But if you would like, please speak with a healthcare professional near you on the information you have read on our website.
  • You should also know that here at Eastview Family Health, we make sure that our own children have all recommended vaccinations, so clearly, we are very confident in vaccinations.

While at the hospital, find out if a doctor, clinical officer or nurse is available to speak with you about vaccines. If not, you can make an appointment to speak to one later. You can also do some reading by yourself on vaccine safety. As you self study, keep in mind that there is a lot of false information about vaccination on the internet. Therefore, it is best for you to use only websites from reputable organizations such as the ones below.

  • World Health Organization
  • U.S. Centres for Disease Control and Prevention. Visit Website ->
  • Immunization Action Coalition. Visit Website->
  • Other credible websites, especially in the national language(s), including the website of your country’s Ministry of Health. Here you are likely to find well-done national publications with solid information on immunization.

This information on vaccines for babies and children was sourced, then aggregated and edited by our team of health professionals. The key sources are:

  1. United Nations Children’s Fund, ‘IPC for Immunization Package’, UNICEF, New York, 2019.
  2. Immunize.Org (IAC). (n.d.). Vaccine Information You Need From The Immunization Action Coalition. Vaccineinformation.Org. Retrieved June 30, 2022, from https://vaccineinformation.org/

  3. N. Sivarajah, S. Sivayogan, J. Jegatheesan, V. Gnananathan BCG vaccination and development of a scar
    Ceylon Med. J., 35 (1990), pp. 75-77
  4. R.S. Vallishayee, a. N. Shashidhara, K. Bunch-Christensen, J. Guld Tuberculin sensitivity and skin lesions in children after vaccination with 11 different BCG strains
    Bull. World Health Organ., 51 (1974), pp. 489-494
  5. C.S. Benn, A. Roth, M.L. Garly, A.B. Fisker, F. Schaltz-Buchholzer, A. Timmermann, et al. BCG scarring and improved child survival: a combined analysis of studies of BCG scarring
    J. Intern. Med. (2020)

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