BCG Vaccine

The Bacillus Calmette-Guérin (BCG) vaccine is a vaccine used to prevent tuberculosis (TB). Here’s some information about the BCG vaccine:


The BCG vaccine contains a weakened strain of Mycobacterium bovis, a bacterium closely related to Mycobacterium tuberculosis, which causes TB in humans. The vaccine is named after the scientists Albert Calmette and Camille Guérin, who developed it in the early 20th century.


The BCG vaccine provides variable levels of protection against TB, particularly in children. It is most effective in preventing severe forms of TB, such as TB meningitis and disseminated TB in children. However, its efficacy in preventing pulmonary TB (the most common form of TB) in adults is variable and generally lower.


The BCG vaccine is typically administered as a single intradermal injection (into the top layers of the skin) on the upper arm. It is often given to infants shortly after birth in countries with a high burden of TB. In some cases, it may also be given to older children or adults who are at high risk of TB infection or progression to active disease.

Side Effects

The BCG vaccine is generally safe, and serious side effects are rare. Common side effects include a small red bump at the injection site, which may develop into a sore or ulcer. Lymph node enlargement in the armpit or neck region can also occur. These side effects usually resolve on their own without treatment.


The BCG vaccine has certain limitations. It does not provide lifelong immunity against TB, and its protective effect can wane over time. Additionally, the BCG vaccine can interfere with the interpretation of the tuberculin skin test (Mantoux test), leading to false-positive results. This can complicate the diagnosis of latent tuberculosis infection (LTBI) in individuals who have received the BCG vaccine.

Geographic Variations

BCG vaccination practices vary worldwide. Some countries with a high burden of TB routinely administer the BCG vaccine to all infants, while others restrict it to high-risk groups or do not recommend it at all.

It’s important to note that the BCG vaccine does not offer complete protection against TB, especially the pulmonary form of the disease, which is the most common. Therefore, individuals who have received the BCG vaccine should still follow TB prevention measures, such as avoiding close contact with individuals with active TB, practicing good respiratory hygiene, and seeking medical evaluation if symptoms of TB develop.

If you have specific concerns or questions about the BCG vaccine, it is recommended to consult with a healthcare professional or your local public health authorities, who can provide up-to-date information and guidance based on your individual circumstances.

Mantoux Test

A Mantoux test is conducted prior to administering the BCG vaccine for anyone over 6 years of age, or younger if they have been in contact with someone who has TB. This test, also known as the tuberculin skin test (TST), is performed to determine if an individual has been exposed to the bacteria that cause tuberculosis (TB). A small amount of tuberculin purified protein derivative (PPD) is injected into the forearm, and the test site is evaluated after 48 to 72 hours for any reaction, typically induration (raised area) at the injection site.  The purpose is to evaluate whether an individual has been previously exposed to tuberculosis. If the Mantoux test result is positive,  it can suggest a past TB exposure or a past  BCG vaccine. However, if the Mantoux test result is negative or shows no significant reaction, it may indicate the absence of TB exposure, and the BCG vaccine may be recommended.

Test Procedure

The Mantoux test involves injecting a small amount of tuberculin purified protein derivative (PPD) into the inner surface of the forearm. This is done using a thin needle and a syringe. The PPD contains proteins derived from the Mycobacterium tuberculosis bacteria. After the injection, a small raised bump or wheal should form at the injection site.

Test Reading

The test is read between 48 and 72 hours after the injection. A trained healthcare professional will measure the size of the induration (raised area) at the injection site using a ruler. Redness or swelling alone is not considered positive unless there is also induration.

Interpretation of Results

The interpretation of the Mantoux test depends on the size of the induration. A positive result suggests exposure to Mycobacterium tuberculosis but does not necessarily mean active TB disease. The cutoff for a positive result varies depending on factors such as age, risk factors, and immune status. Generally, an induration of 5 mm or greater is considered positive for certain high-risk groups (e.g., HIV-positive individuals, close contacts of active TB cases), while a cutoff of 10 mm or greater is used for most other individuals.


A positive Mantoux test can indicate TB disease . Further evaluation is needed, including a chest X-ray and blood test, to determine if active TB disease is present.


The Mantoux test has some limitations. False-positive results can occur due to prior BCG vaccination or exposure to non-tuberculosis mycobacteria. False-negative results can occur in individuals with weakened immune systems or if the test is read too early or too late.

It’s important to note that the Mantoux test is one of several tools used in the diagnosis and management of tuberculosis. Interpretation of the test results should be done by a qualified healthcare professional experienced in tuberculosis diagnosis and management.

If you suspect exposure to tuberculosis or have concerns about your health, it’s best to consult with a healthcare professional for evaluation, testing, and appropriate follow-up care.