BCG vaccination

Immunization strategy and vaccine types

Tuberculosis vaccination is based on administering an attenuated strain of Mycobacterium bovis (bacillus Calmette–Guerin). The strategy for choosing a specific preparation always depends on the current epidemiological situation in the region of residence and the child's individual health status.

Two vaccine options are used for primary immunization of newborns:

• BCG-M is a reduced-dose preparation. It is used as the standard of care for primary tuberculosis prevention in the majority of children.
• BCG is a standard vaccine with full antigenic load. Its use is justified and necessary in regions with an unfavorable epidemiological situation (where the incidence exceeds 80 cases per 100,000 population), as well as in situations where close contact with a tuberculosis patient has been reliably identified in the newborn's immediate environment.

Revaccination and pharmacological effects

Re-administration of the vaccine (revaccination) is performed exclusively with the BCG vaccine at strictly scheduled intervals—when the child turns 7 or 14 years old. A mandatory prerequisite for revaccination is the complete absence of infection with Mycobacterium tuberculosis, which must be confirmed by negative results from prior tuberculin skin tests.

Administration of the vaccine triggers a cascade of pharmacological and immunological reactions:

1. Specific humoral (antibody-mediated) immunity against the specific pathogen is formed.
2. Full cellular immunity develops and immunological memory is established.
3. The primary goal is achieved—a reduction in overall morbidity and a significant decrease in the severity of the infection in the event of actual exposure to the wild-type pathogen.
4. Local inflammation occurs at the injection site. This is a completely natural stage in the development of an adequate immune response. Normally, a specific papule (the so-called "orange peel") forms on the skin, and its development may be accompanied by local tissue necrosis.
5. Post-vaccination tuberculin allergy develops—a normal immune response to the administered preparation, which must later be carefully differentiated from true infection.

Clinical interpretation of tests and Diaskintest

A positive reaction to the classic Mantoux test is not a definitive sign of disease and always requires competent differential diagnosis. A positive reaction can develop for two completely different reasons:

• Infectious allergy is the result of true infection of the body with the wild-type strain of Mycobacterium tuberculosis.
• Post-vaccination allergy is a completely normal immune response resulting from prior primary vaccination or revaccination with the BCG vaccine.

To overcome the limitations of the Mantoux test and accurately distinguish between these two conditions, an innovative method is used — Diaskintest.

It contains a recombinant tuberculosis allergen comprising two specific antigens: CFP10 and ESAT6. The mechanism of the test's high specificity is that these antigens are present only in virulent strains of M. tuberculosis and M. bovis. At the same time, they are completely absent in BCG vaccine strains and the vast majority of nontuberculous mycobacteria.

The advantages of Diaskintest lie in its exceptionally high sensitivity and specificity. In clinical practice, it is used for:

• Accurate diagnosis of tuberculosis and assessment of the activity of the pathological process.
• Differential diagnosis (to distinguish between a vaccine reaction and true infection).
• Close monitoring of the effectiveness of ongoing treatment.

The Diaskintest result will be negative in individuals vaccinated with BCG (unless they are infected with the wild-type strain) and in completely uninfected people. Important to remember: this test is strictly not used to screen patients for BCG vaccination or revaccination, as it is fundamentally incapable of detecting established immunity to the vaccine itself.

Class and exam questions

What else to study on this topic

• CFP10 and ESAT6 antigens: structure and role in the pathogenesis of tuberculosis
• Mechanisms of cellular immunity development in mycobacterial infections
• Differential diagnosis of post-vaccination and infectious allergies
• Criteria for assessing the activity of the tuberculosis process
• Monitoring the effectiveness of anti-tuberculosis chemotherapy

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.